Tensioned meniscus prosthetic devices and associated methods

ABSTRACT

A prosthetic device for use as an artificial meniscus is disclosed. The prosthetic device restores shock absorption, stability, and function to the knee joint after removal of the damaged natural meniscus. In some embodiments, the prosthetic device is pre-tensioned to improve the fit of the prosthetic device within the knee joint and, thereby, maximize the contact area of the load-bearing surfaces to distribute loading through the prosthetic device in a manner substantially similar to that of a healthy natural meniscus. In some embodiments, the pre-tensioned prosthetic device is smaller, or scaled-down, relative to the size of a healthy natural meniscus.

BACKGROUND

The present disclosure generally relates to medical prosthetic devices,systems, and methods. More specifically, in some instances the presentdisclosure relates to prosthetic devices that replace at least part ofthe functionality of the natural meniscus. Each knee has two menisci, alateral meniscus and a medial meniscus. Each meniscus is acrescent-shaped fibrocartilaginous tissue attached to the tibia at ananterior and a posterior horn. Damage to the meniscus can cause pain andarthritis. Accordingly, in some instances it is desirable to replace thedamaged natural meniscus with a prosthetic device. In some instances theprosthetic devices of the present disclosure are configured to besurgically implanted into a knee joint to replace or augment the naturalmeniscus. It is important that the prosthetic device be of theappropriate size and functionality for the intended patient. In someinstances the methods of the present disclosure identify suitableprosthetic devices for use with a particular patient.

While existing devices, systems, and methods have attempted to addressthese issues, they have not been satisfactory in all respects.Accordingly, there is a need for the improved devices, systems, andmethods in accordance with the present disclosure.

SUMMARY

In one embodiment, a meniscus prosthetic device is disclosed.

In another embodiment, a prosthetic device for replacing a damagedmeniscus is disclosed. The prosthetic device comprises a central portionhaving an upper surface for engagement with a portion of a femur and anopposing lower surface for engagement with a portion of a tibia. Thecentral portion comprises a resilient material. The prosthetic devicealso includes an outer portion surrounding the central portion andhaving an increased thickness relative to the central portion. The outerportion comprises the resilient material and tensioned with at least onereinforcing fiber embedded in the resilient material. The outer portionis sized and shaped such that a compression force imparted on theprosthetic device by the femur and the tibia urges the outer portionradially outward from the central portion.

In another embodiment, a meniscus prosthetic device for use in a kneejoint is disclosed. The meniscus prosthetic device comprises a centralportion having an upper surface for engagement with a portion of a femurand an opposing lower surface for engagement with a portion of a tibia.The central portion comprises a resilient polycarbonate polyurethane.The meniscus prosthetic device also includes an outer portionsurrounding the central portion and having an increased thicknessrelative to the central portion. The outer portion comprises a resilientpolycarbonate polyurethane embedded with tensioned ultra high molecularweight polyethylene reinforcing fibers. The outer portion has a firstsection with a semi-ellipsoidal profile similar to a natural meniscusand a second section connecting the ends of the first section. Thesecond section is sized and shaped to engage the femur notch to securethe meniscus prosthetic device within the knee joint without penetratingbone.

In another embodiment, a meniscus implant is disclosed. The meniscusimplant comprises a central portion having an upper surface forengagement with a portion of a femur and an opposing lower surface forengagement with a portion of a tibia. The central portion comprises aresilient polycarbonate polyurethane and is resiliently deformablebetween an unloaded position and a loaded position. The upper and lowersurfaces of the central portion have increased contact with the femurand the tibia in the loaded position. The meniscus implant also includesan outer portion surrounding the central portion and having an increasedthickness relative to the central portion. The outer portion comprisinga resilient polycarbonate polyurethane embedded with tensioned ultrahigh molecular weight polyethylene reinforcing fibers. The outer portionincludes a first section having a generally semi-ellipsoidal profilesimilar to a natural meniscus and a second section connecting the endsof the first section. The second section is sized and shaped to engage afemur notch to secure the meniscus prosthetic device within the kneejoint without penetrating bone. The outer portion is resilientlydeformable between an unloaded position and a loaded position. At leasta section of the outer portion is displaced radially outward from thecentral portion in the loaded position.

In another embodiment, a prosthetic device for replacing a damagedmeniscus of a knee joint is disclosed. The prosthetic device comprises acentral portion having an upper surface for engagement with a portion ofa femur and an opposing lower surface for engagement with a portion of atibia. The central portion is formed of a resilient polyurethane. Theprosthetic device also includes an outer portion surrounding the centralportion and having an increased thickness relative to the centralportion. The outer portion comprises a first section having a generallysemi-ellipsoidal profile similar to that of a natural meniscus and asecond section extending between first and second ends of the firstsection. The second section is sized and shaped to engage a femur notchto secure the meniscus prosthetic device within the knee joint withoutpenetrating bone. The outer portion is formed of the resilientpolyurethane embedded with reinforcing fibers such that the outerportion has an increased stiffness relative to the central portion.

In another embodiment, a meniscus prosthetic device is disclosed. Themeniscus prosthetic devices comprises a central portion having an uppersurface for engagement with a portion of a femur and an opposing lowersurface for engagement with a portion of a tibia. An outer portionsurrounds the central portion and has an increased thickness relative tothe central portion. The outer portion comprises a first section havinga generally semi-ellipsoidal profile similar to that of a naturalmeniscus and a second section extending between first and second ends ofthe first section. The second section is sized and shaped to engage afemur notch to secure the meniscus prosthetic device within a knee jointwithout penetrating bone. The second section has an upper-inner surfacetapering into the upper surface of the central portion. The upper-innersurface is defined by a varying radius of curvature along a length ofthe second section.

In another embodiment, a meniscus implant for secured positioning withina knee joint without requiring the penetration of bone is disclosed. Themeniscus implant comprises a central portion having an upper surface forengagement with a portion of a femur and an opposing lower surface forengagement with a portion of a tibia. An outer portion surrounds thecentral portion and has an increased thickness relative to the centralportion. The outer portion comprises a first section having a generallysemi-ellipsoidal profile similar to that of a natural meniscus and asecond section extending between first and second ends of the firstsection. The second section has a first region adjacent the first end ofthe first section, a second region adjacent the second end of the firstsection, and third region between the first and second regions. Thefirst region of the second section has a height between about 4 mm andabout 15 mm, a first radius of curvature along the length of the secondsection between about 5 mm and about 70 mm, and a second radius ofcurvature perpendicular to the length of the second section betweenabout 10 mm and about 100 mm. The second region of the second sectionhas a height between about 4 mm and about 15 mm, a third radius ofcurvature along the length of the second section between about 5 mm andabout 50 mm, and a fourth radius of curvature perpendicular to thelength of the second section between about 5 mm and about 70 mm. Thethird region of the second section has a height between about 4 mm andabout 15 mm and a first radius of curvature along the length of thesecond section between about 10 mm and about 30 mm.

In another embodiment, a method of manufacturing a meniscus prostheticdevice is disclosed. The method comprises injection molding a corehaving an upper surface, a lower surface opposite the upper surface, andan outer surface disposed between the upper and lower surfaces. Theouter surface defines a plurality of recesses. The method also includeswinding reinforcing fiber into at least one of the plurality of recessesof the outer surface and injection molding an outer portion around theouter surface and the reinforcing fibers to secure the reinforcingfibers therein. In one aspect, the material of the core has a highermelting point than the reinforcing fibers.

In another embodiment, a method of manufacturing a prosthetic device isdisclosed. The method comprises injecting a polycarbonate polyurethaneinto a mold to form a core. The mold comprises a mirror polished uppermolding surface for defining an upper surface of the core, a mirrorpolished lower molding surface for defining a lower surface of the core,and one or more removable inserts for defining a plurality of recessesof the core. The method includes removing the one or more removableinserts and winding ultra high molecular weight polyethylene reinforcingfiber around the core and into at least one of the plurality of recessesof the core. The method also includes heating the core, injecting apolycarbonate polyurethane into the mold to form an outer layersurrounding the core and the reinforcing fiber, and cooling the mold. Insome instances, the polycarbonate polyurethane has a higher meltingpoint than the polyethylene reinforcing fibers such that thepolycarbonate polyurethane is injected at a temperature above themelting point of the polyethylene reinforcing fibers.

In another embodiment, a method of forming a meniscus implant isdisclosed. The method comprises injecting a polymer into a mold to forma core. The mold comprises a mirror polished upper molding surface fordefining an upper surface of the core, a mirror polished lower moldingsurface for defining a lower surface of the core, and one or moreremovable inserts for defining a plurality of recesses around aperimeter of the core. The method also includes removing the one or moreremovable inserts and winding reinforcing fiber around the core and intothe plurality of recesses of the core. The reinforcing fiber istensioned with a force between about 5 N and about 78 N during thewinding. The method also includes injecting a polymer into the mold toform an outer layer surrounding the core and the reinforcing fiber.

In another embodiment, a method of selecting a meniscus prostheticdevice for a patient from a library of available prosthetic devices isdisclosed. The method comprises a pre-implantation matching process. Thepre-implantation matching process comprises a direct geometricalmatching process, a correlation parameters-based matching process, and afinite element-based matching process. The direct geometrical matchingprocess comprises obtaining an image of the patient's healthy knee,segmenting the knee into components, including a healthy meniscus, andcomparing the healthy meniscus to the available prosthetic devices toidentify any geometrically suitable prosthetic devices. The correlationparameters-based matching process comprises obtaining an image of thepatient's injured knee, determining one or more correlation parametersfor the available prosthetic devices based on anatomical measurements ofthe injured knee, and comparing the one or more correlation parametersfor the available prosthetic devices to an accepted normative data rangeto identify any correlation-parameter suitable prosthetic devices.Finally, the finite element-based matching process comprises creating afinite element model of the patient's injured knee based on the image ofthe patient's injured knee, simulating a loading of the patient'sinjured knee with an available prosthetic device positioned therein forone or more of the available prosthetic devices, and evaluating a loaddistribution for the one or more of the available prosthetic devices toidentify any finite-element suitable prosthetic devices.

In another embodiment, a method of treating a damaged meniscus isdisclosed. The method comprises utilizing a pre-implantation matchingprocess to identify a best suitable meniscus prosthetic device forreplacing the damaged meniscus. The pre-implantation matching processcomprises a correlation parameters-based matching process that considersan area correlation, a width correlation, a length correlation, and aperimeter correlation. The area correlation is defined by a meniscuscontact area divided by a medial tibia area. The width correlation isdefined by an average meniscus width divided by a medial tibia width.The length correlation is defined by a medial meniscus length divided bya medial tibia length. The perimeter correlation is defined by ameniscus perimeter divided by a medial tibia perimeter.

In another embodiment, a surgical method is disclosed. The surgicalmethod comprises performing an arthroscopy to create a medial portal,excising a majority of a damaged meniscus, excising a portion of a fatpad, enlarging the medial portal to a diameter between about 4.0 cm andabout 6.0 cm, accessing a medial cavity, trialing one or more implanttrials to identify a most suitable meniscus prosthesis, and implantingand securing the most suitable meniscus prosthesis into the medialcavity without penetrating bone with the implant.

In another embodiment, a biocompatible composite material is molded fromat least two materials having different melting points. In one aspect,the first material is heated above the melting point of the secondmaterial and molded around the second material.

BRIEF DESCRIPTION OF DRAWINGS

Other features and advantages of the present disclosure will becomeapparent in the following detailed description of embodiments of thedisclosure with reference to the accompanying of drawings, of which:

FIG. 1 is a diagrammatic perspective view of an embodiment of aprosthetic device according to one embodiment of the present disclosure.

FIG. 2 is a diagrammatic top view of the prosthetic device of FIG. 1.

FIG. 3 is a diagrammatic cross-sectional view of the prosthetic deviceof FIGS. 1 and 2 taken along section line 3-3.

FIG. 4 is a diagrammatic cross-sectional view of the prosthetic deviceof FIGS. 1 and 2 taken along section line 4-4.

FIG. 5 is a diagrammatic cross-sectional comparison view of theprosthetic device of FIGS. 1 and 2 and an alternative prosthetic device.More specifically, FIG. 5 is a cross-sectional view of the prostheticdevice of FIGS. 1 and 2 taken along section line 4-4 shown in comparisonto a diagrammatic cross-sectional view of an alternative prostheticdevice taken along a corresponding cross-section line.

FIG. 6 is a diagrammatic cross-sectional view of the prosthetic deviceof FIGS. 1 and 2 taken along section line 6-6.

FIG. 7 is a diagrammatic cross-sectional view of the prosthetic deviceof FIGS. 1 and 2 taken along section line 7-7.

FIG. 8 is a diagrammatic cross-sectional comparison view of theprosthetic device of FIGS. 1 and 2 and an alternative prosthetic device.More specifically, FIG. 8 is a cross-sectional view of the prostheticdevice of FIGS. 1 and 2 taken along section line 8-8 shown in comparisonto a diagrammatic cross-sectional view of an alternative prostheticdevice taken along a corresponding cross-section line.

FIG. 9 a is a diagrammatic cross-sectional view of the prosthetic deviceof FIGS. 1 and 2 positioned between a femur and a tibia in an insertionconfiguration.

FIG. 9 b is a diagrammatic cross-sectional view of the prosthetic deviceof FIGS. 1 and 2 positioned between a femur and a tibia in apre-tensioned, unloaded state.

FIG. 10 is a diagrammatic cross-sectional view of the prosthetic deviceof FIGS. 1 and 2 positioned between a femur and a tibia similar to thatof FIG. 9 b, but showing the prosthetic device in a loaded,weight-bearing state.

FIG. 11 is a block diagram of an embodiment of a method according to oneaspect of the present disclosure for selecting an appropriate prostheticdevice for use with a patient's knee.

FIG. 12 is a block diagram of an embodiment of a method according to oneaspect of the present disclosure for selecting an appropriate prostheticdevice for use with a patient's knee prior to surgery.

FIG. 13 is a diagrammatic side view of a rendering knee joint where thebone, articular cartilage, and meniscus have been segmented according toone aspect of the present disclosure.

FIG. 14 is a diagrammatic perspective view of a three-dimensionalreconstruction of a natural meniscus according to one aspect of thepresent disclosure.

FIG. 15 is a chart setting forth various correlation parametersaccording to one aspect of the present disclosure.

FIG. 16 is a cross-sectional top view of a knee joint based on an MRIand/or CT scan of the knee joint identifying measurements of theanatomical features of the knee joint according to one aspect of thepresent disclosure.

FIG. 17 is a cross-sectional top view of a knee joint based on an MRIand/or CT scan of the knee joint similar to that of FIG. 16, butidentifying measurements of other anatomical features according to oneaspect of the present disclosure.

FIG. 18 is a cross-sectional sagittal view of a knee joint based on anMRI and/or CT scan of the knee joint identifying a medial meniscusheight according to one aspect of the present disclosure.

FIG. 19 is a cross-sectional side view of a knee joint based on an MRIand/or CT scan of the knee joint identifying anterior and posteriormeniscus heights according to one aspect of the present disclosure.

FIG. 20 is a diagrammatic perspective view of a three-dimensional finiteelement model of a knee joint according to one aspect of the presentdisclosure.

FIG. 21 is a rendering of a simulated contact pressure map between aprosthetic device and a tibialis plateau according to one aspect of thepresent disclosure.

FIG. 22 is a diagrammatic perspective view of a prosthetic device foruse in replacing a damaged natural meniscus according to the presentdisclosure shown in comparison to the dimensions of a healthy naturalmeniscus.

FIG. 23 is a block diagram of an embodiment of a method according to oneaspect of the present disclosure for selecting an appropriate prostheticdevice for use with a patient's knee during surgery.

FIG. 24 is a block diagram of a surgical protocol according to oneaspect of the present disclosure.

FIG. 25 is a block diagram of a method for implanting a prostheticdevice into a patient's knee for use in the surgical protocol of FIG. 24according to one aspect of the present disclosure.

FIG. 26 is a block diagram of a method for implanting a prostheticdevice into a patient's knee for use in the surgical protocol of FIG. 24according to another aspect of the present disclosure.

FIG. 27 is a diagrammatic perspective view of a prosthetic deviceaccording to one aspect of the present disclosure.

FIG. 28 is a diagrammatic perspective view of a core of a prostheticdevice according to one aspect of the present disclosure.

FIG. 29 is a diagrammatic perspective view of a core of the prostheticdevice of FIG. 27 according to one aspect of the present disclosure.

FIG. 30 is a diagrammatic cross-sectional view of the prosthetic devicecore of FIG. 29.

FIG. 31 is a diagrammatic perspective view of an outer portion of theprosthetic device of FIG. 27 according to one aspect of the presentdisclosure.

FIG. 32 is a chart setting forth fiber incorporation ratios forprosthetic devices based on patient weight and activity levels accordingto one aspect of the present disclosure.

FIG. 33 is a diagrammatic cross-sectional view of a prosthetic devicehaving a fiber density according to one aspect of the presentdisclosure.

FIG. 34 is a diagrammatic cross-sectional view of a prosthetic devicesimilar to that of FIG. 38, but having an alternative fiber densityaccording to one aspect of the present disclosure.

FIG. 35 is a block diagram of a method for manufacturing a prostheticdevice according to one aspect of the present disclosure.

FIG. 36 is a chart setting forth tensioning forces for windingreinforcement fibers around a core of a prosthetic device according toone aspect of the present disclosure.

FIG. 37 is a diagrammatic perspective view of a material having a linearfiber configuration according to one aspect of the present disclosure.

FIG. 38 is a diagrammatic perspective view of a material having a fibermesh configuration according to one aspect of the present disclosure.

FIG. 39 is a diagrammatic partial cross-sectional view of the materialhaving a fiber mesh configuration of FIG. 38 taken along section line39-39.

FIG. 40 is a diagrammatic perspective view of a material having a windedfiber configuration according to one aspect of the present disclosure.

FIG. 41 is a diagrammatic partial perspective cross-sectional view ofthe material having a winded fiber configuration of FIG. 40 taken alongsection line 41-41.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the illustrated embodiments. It is nevertheless understood thatno limitation of the scope of the disclosure is intended. Any and allalterations or modifications to the described devices, instruments,and/or methods, as well as any further application of the principles ofthe present disclosure that would be apparent to one skilled in the artare encompassed by the present disclosure even if not explicitlydiscussed herein. Further, it is fully contemplated that the features,components, and/or steps described with respect to one embodiment may becombined with the features, components, and/or steps described withrespect to other embodiments of the present disclosure.

Prosthetic Devices

Referring now to FIGS. 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 shown thereinis a prosthetic device 100 according to one aspect of the presentdisclosure. In particular, FIG. 1 is a diagrammatic perspective view ofthe prosthetic device 100. FIG. 2 is a diagrammatic top view of theprosthetic device 100. FIGS. 3, 4, 5, 6, 7, and 8 show variouscross-sectional views of the prosthetic device 100. FIG. 3 is adiagrammatic cross-sectional view of the prosthetic device 100 takenalong section line 3-3 of FIG. 2. FIG. 4 is a diagrammaticcross-sectional view of the prosthetic device 100 taken along sectionline 4-4 of FIG. 2. FIG. 5 is a diagrammatic cross-sectional comparisonview of the prosthetic device 100 with an alternative prosthetic device102. More specifically, FIG. 5 is a cross-sectional view of theprosthetic device 100 taken along section line 4-4 of FIG. 2 shown incomparison to a cross-sectional view of the alternative prostheticdevice 102 taken along a corresponding cross-section line. FIG. 6 is adiagrammatic cross-sectional view of the prosthetic device 100 takenalong section line 6-6 of FIG. 2. FIG. 7 is a diagrammaticcross-sectional view of the prosthetic device 100 taken along sectionline 7-7 of FIG. 2. FIG. 8 is a diagrammatic cross-sectional comparisonview of the prosthetic device 100 with the alternative prosthetic device102 similar to that of FIG. 5, but taken along a different section line.More specifically, FIG. 8 is a cross-sectional view of the prostheticdevice 100 taken along section line 8-8 of FIG. 2 shown in comparison toa cross-sectional view of the alternative prosthetic device 102 takenalong a corresponding cross-section line. FIG. 9 a is a diagrammaticcross-sectional view of the prosthetic device of FIGS. 1 and 2positioned between a femur and a tibia in an insertion configuration.FIG. 9 b is a diagrammatic cross-sectional view of the prosthetic device100 positioned between a femur 104 and a tibia 106 in a pre-tensioned,unloaded state. FIG. 10 is a diagrammatic cross-sectional view of theprosthetic device 100 positioned between the femur 104 and the tibia 106similar to that of FIG. 9 b, but showing the prosthetic device 100 in aloaded, weight-bearing state.

Generally, the prosthetic device 100 is for the replacement of ameniscus that has been damaged, ruptured, disintegrated, diseased, or isotherwise in need of replacement. For illustrative purposes, theprosthetic device 100 will be described in conjunction with a rightknee, medial meniscus replacement. However, corresponding embodimentsare utilized for replacement of any of the other menisci, such as theleft knee medial meniscus, left knee lateral meniscus, and/or right kneelateral meniscus. In that regard, the size, shape, thickness, materialproperties, and/or other properties of the prosthetic device may beconfigured for each particular application.

The prosthetic meniscus 100 comprises an outer body portion 108 and acentral body portion 110. Generally, the outer body portion 108 has anincreased thickness and height relative to the central body portion 110.In some instances the outer body portion 108 has a thickness between 5mm and 15 mm. In some instances, the central body portion 110 has athickness between 0.1 mm and 5 mm. In one particular embodiment, theouter body portion 108 has a maximum thickness of approximately 10 mmand the central body portion 110 has a maximum thickness ofapproximately 2 mm. The height or thickness of the outer body portion108 varies around the perimeter of the prosthetic device 100 in someinstances. In that regard, the variations in the height or thickness ofthe outer body portion 108 are selected to match the anatomical featuresof the patient in some embodiments. Similarly, the height or thicknessof the central body portion 110 varies across the prosthetic device 100in some embodiments. Again, the variations in the height or thickness ofthe central body portion 110 are selected to match the anatomicalfeatures of the patient in some embodiments. In some embodiments, theprosthetic device 100 is inserted in an insertion configuration and thenloaded, stretched, moved, and/or otherwise transferred to animplantation configuration. In some embodiments the transformationbetween the insertion configuration and the implantation configurationis facilitated through the load bearing of the prosthetic device 100. Insuch embodiments, the variations in height or thickness of the outer andcentral body portions 108, 110 are selected to accommodate thedeformation or transformation between the insertion configuration andthe implantation configuration.

In the present embodiment, the prosthetic device 100 is configured foruse without a fixation member or fixation device that would penetrate anadjacent bone to keep the prosthetic device in place. Rather, theprosthetic device 100 is configured to “float” within the knee jointwithout being secured by such bone-penetrating fixation devices orotherwise rigidly fixed to the femur or tibia. To that end, the outerbody portion 108 of the prosthetic device 100 is shaped and sized toprevent unwanted expulsion of the prosthetic device 100 from the kneejoint. The prosthetic device 100 is implanted into a patient withoutcausing permanent damage to the patient's tibia or other bonestructure(s) engaged by the prosthetic device in some embodiments. Insome instances the prosthetic device 100 is implanted to alleviate thepatient's knee problems while avoiding permanent destruction of thepatient's anatomy, such as cutting or reaming a large opening in thetibia. In such instances, the prosthetic device 100 may be subsequentlyremoved and replaced with another prosthetic device or treatment withoutadversely affecting the subsequent treatment.

To this end, the outer body portion 108 of the prosthetic device 100includes a first portion 112 and a second portion or bridge 114. In someembodiments, the first portion 112 substantially matches the shape of anatural meniscus. In some embodiments, the outer body portion 108 has asemi-ellipsoidal shape. Accordingly, the first portion 112 extendsaround a majority of the outer body portion 108. The bridge 114 connectsthe two ends of the first portion 112. Thus, where the prosthetic deviceis configured for use as a medial meniscus device, the bridge 114extends along the lateral side of the device. Where the prostheticdevice 100 is configured for use as a lateral meniscus device, thebridge 114 extends along the medial side of the device. Accordingly, theouter body portion 108—comprised of the first portion 112 and the bridge114 and having an increased thickness relative to the central bodyportion 110—completely surrounds the central body portion 110 and servesto limit movement of the prosthetic device 100 after implantation. Thatis, the increased height of the outer body portion 108 along with thecontact pressure on the prosthetic device 100 from being positionedbetween the femur and the tibia prevents the prosthetic device frommoving outside of the desired range of positions within the knee joint.In some instances, a distal portion of the femur is received within theupper recess defined by the outer body portion 108 and maintained withinthe recess by the increased height of the outer body portion 108 and thecontact pressure on the device 100.

The height or thickness of the bridge component 114 is based on the sizeof the femur notch and the distance to the cruciate ligaments in someembodiments. In some embodiments, the bridge 114 has a maximum height orthickness that is between ¼ and ¾ the maximum height or thickness of thefirst portion 112 of the outer body portion 108. In some embodiments,the size and shape of the bridge 114 is selected to achieve an optimalpressure distribution on the tibialis plateau in order to mimic thepressure distribution of a healthy natural meniscus. The bridge 114 and,more generally, the outer body portion 108 are geometricallycharacterized by anterior, posterior, lateral-anterior, mid-lateral andlateral-posterior angles and heights as well as sagittal and coronalradii of curvature. Specific typical ranges of sizes, shapes, angles,radii of curvature, and other geometrical attributes of the bridge 114will be discussed below with respect to FIGS. 3, 4, 6, and 7. Whilethese ranges are understood to encompass the majority of ranges utilizedin treating patients, no limitation is intended thereby. It is certainlycontemplated that there are situations and/or applications where use ofcomponents outside of these ranges will be desirable or necessary.

Further, the outer body portion 108 and the central body portion 110 areshaped and sized such that the prosthetic device 100 is self-centering.That is, the shape and size of the prosthetic device 100 itselfencourages the prosthetic device 100 to position or align itself with adesired orientation within the knee joint. Accordingly, as theprosthetic device 100 moves through a range of positions within the kneejoint it naturally returns to the desired orientation due to the shapeand size of the outer and central body portion 108, 110. In someembodiments, the outer body portion and, more specifically, the bridge114 acts as a physical barrier limiting the movement of the prostheticdevice caused by joint reaction forces. The self-centering orself-aligning mechanism combined with the prosthetic device's ability tomove within the knee joint results in improved location of theprosthetic device 100 during typical load-bearing gait cycles (e.g.,flexion-extension angles of 0° to 20° or “heel-strike” to “toe-off”).The result is that the prosthetic device 100 exhibits a load pressuredistribution similar to that of a natural meniscus.

The central body portion 110 defines an upper surface 116 and a lowersurface 118. The upper and lower surfaces 116, 118 are both articulatingbearing surfaces. In particular, the upper and lower surfaces 116, 118are configured to movingly engage with the femur and tibia,respectively. In that regard, the prosthetic device 100 can translateand rotate with respect to the femur and/or tibia within a range. Insome instances, translation is possible in both the anterior-posteriorand medial-lateral directions. In some embodiments, the upper surface116 includes both a vertical and horizontal bearing components. To thatend, in some embodiments the upper surface 116 comprises a concavesurface that defines the vertical and horizontal bearing components. Thethickness of the central body portion 110 between the upper surface 116and the lower surface 118 supports the vertical bearing component, whilethe increased height of the upper surface 116 as it extends outwardlytowards the outer body portion 108 defines the horizontal bearingcomponent. Similarly, in some embodiments the lower surface 118 includesboth vertical and horizontal bearing components. In particular, in someembodiments the lower surface 118 comprises a convex surface. Thethickness of the central body portion 110 between the upper surface 116and the lower surface 118 supports the vertical bearing component, whilethe tapered height of the lower surface 116 as it extends outwardlytowards the outer body portion 108 defines the horizontal bearingcomponent. In some embodiments, the upper surface 116 and/or the lowersurface 118 are shaped such that the prosthetic device 10 is biasedtowards a neutral position in the knee. For example, the arcuateprofiles of the upper surface 116 and/or the lower surface 116 areshaped such that the interaction between the surfaces and the boneencourages the bone to a particular orientation relative to thesurfaces. This allows the prosthetic device 100 to be self-centering orself-aligning in some embodiments as discussed above with respect to theouter body portion 108.

In some embodiments, the prosthetic device 100 includes one or morerecesses (not shown) in the upper surface 116. The recesses provide forthe accumulation of synovial fluid. In some embodiments, the recessesare positioned at the most prevalent contact points of the femur withthe upper surface 116. In such embodiments, the synovial fluidlubricates the upper articulation surface 116 of the prosthetic deviceto limit the friction between the prosthetic device 100 and the femur.The recesses may have various shapes within the upper surface 116 and,in some instances, are shaped based on the specific anatomical featuresof a patient. In that regard, the recesses may comprise a slopingdepression that creates a concave recess in some embodiments. Theconcave recess may comprise a substantially circular profile, anelongated profile, an irregular shape, and/or combinations thereof. Theprosthetic device 100 includes a various number of recesses in differentembodiments. In some embodiments, the prosthetic device 100 does notinclude any recesses in the upper surface 116 as illustrated in FIG. 1.

As shown in FIGS. 1 and 2, the upper articulation surface 116 is boundedby the outer body portion 108. In that regard, the first portion 112 andthe bridge 114 of the outer body portion 108 define a rim or wall havingan increased height relative to the central body portion 110 such thatthe upper surface 116 is recessed with respect to the outer body portion108. Referring more specifically to FIGS. 3, 4, 6, and 7, in the currentembodiment, the outer body portion 108 defines a substantially convexupper surface 120 that tapers down in to the upper articulation surface116 on one side and to an outer surface 122 of the prosthetic device 100on the other side. Accordingly, the upper surface 116 of the centralbody portion 110 and the taper of the upper surface 120 of the outerbody portion 108 define a concave recess configured for receiving aportion of the femur such as the femoral condyle. Accordingly, in someinstances when the prosthetic device 100 is implanted, the central bodyportion 110 bounded by the outer body portion 108 serves to isolate andcushion the femoral condyle from the tibial plateau. In that regard, theouter body portion 108 serves to limit the movement of the prostheticdevice relative to the femoral condyle. In particular, in the currentembodiment the outer body portion 108 prevents the portion of the femurmovingly engaged with the prosthetic device 100 from moving laterallybeyond the outer body portion 108. In this manner the prosthetic device100 provides shock absorption and a desirable tribology between thefemur and tibia.

Referring more specifically to FIGS. 2-8, typical ranges of sizes,shapes, angles, radii of curvature, and other geometrical attributes ofthe prosthetic device 100 will be discussed. While these ranges areunderstood to encompass the majority of ranges utilized in treatingpatients, no limitation is intended thereby. It is certainlycontemplated that there are situations and/or applications where use ofcomponents outside of these ranges will be desirable or necessary.

Referring more specifically to FIG. 3, shown therein is a diagrammaticcross-sectional view of the prosthetic device 100 taken along sectionline 3-3 of FIG. 2. As shown, in the current embodiment the outer bodyportion 108 includes a plurality of imbedded fibers 124 therein. Theimbedded fibers 124 are utilized in some embodiments to pretension theprosthetic device 100. In some embodiments the imbedded fibers 124 areutilized to increase the stiffness and/or strength of the outer bodyportion 108 relative to the central body portion 110. In someembodiments, the fibers 124 are utilized to both pretension theprosthetic device 100 and to increase the radial stiffness and/or hoopstrength of the outer body portion 108. In some instances, the imbeddedfibers 124 comprise an ultra high molecular weight polyethylene. In oneparticular embodiment, the fibers 124 comprise an ultra high molecularweight polyethylene and are imbedded within a polycarbonate polyurethaneforming at least the outer body portion 108 of the prosthetic device100.

In some instances, the fibers 124 prevent the bridge 114 from splayingoutwardly, which prevents the prosthetic device 100 from being releasedfrom the knee. The fibers 124 tend to transfer the radial outward forcesapplied on the bridge 114 to a portion of the outer body portion 108 onthe opposite side of the prosthetic device 100, which is in contact withthe femur. In this manner, the fibers 124 prevent unwanted movement ofthe prosthetic device 100 and, in particular, prevent the prostheticdevice from slipping or popping out of the knee joint. During insertion,however, the bridge 114 may be folded inwardly into an insertionconfiguration (see FIG. 9 a for example) as the fibers do not resistinwardly directed radial or compressive forces. Once the bridge 114 isinserted past the bearing condyle surfaces and adjacent to the femoralnotch, the resilient properties of the prosthetic device's core materialcauses the bridge to spring outwardly into an anchoring configuration(see FIG. 9 b for example).

As shown in FIG. 3, the first portion 112 of the outer body portion 108has a height or thickness 126 at cross-sectional line 3-3. In thatregard, the height or thickness 126 of the first portion 112 is betweenabout 4 mm and about 15 mm and, in some instances, between about 5.7 mmand about 9.3 mm. In the present embodiment, the height or thickness 126of the first portion 112 is approximately 7.6 mm. In a smallerembodiment, the height or thickness 126 is approximately 5.7 mm. In alarger embodiment, the height or thickness 126 is approximately 9.3 mm.In the present embodiment, configured for use as a medial meniscusreplacement, the height or thickness 126 may be considered amedial-anterior height or thickness of the first portion 112 of theouter body portion 108. In a lateral meniscus replacement, thecorresponding height or thickness of a similar prosthetic deviceconfigured for the lateral replacement may be within a similar range andbe considered a lateral anterior height or thickness of the outer bodyportion.

Similarly, the bridge 114 of the outer body portion 108 has a height orthickness 128 at cross-sectional line 3-3. The height or thickness 128of the bridge 114 is also between about 4 mm and about 15 mm and, insome instances, between about 5.1 mm and about 8.8 mm. In the presentembodiment, the height or thickness 128 of the bridge 114 isapproximately 7.0 mm. In a smaller embodiment, the height or thickness128 is approximately 5.1 mm. In a larger embodiment, the height orthickness 128 is approximately 8.8 mm. In the present embodiment,configured for use as a medial meniscus replacement, the height orthickness 128 may be considered a lateral-anterior height or thicknessof the bridge 114. In a lateral meniscus replacement, the correspondingheight or thickness of a similar prosthetic device configured for thelateral replacement may be within a similar range and be considered amedial anterior height or thickness of the bridge.

An inner surface 130 of the bridge 114 connects the bridge 114 to theupper articulating surface 116 of the central body portion 110. Theinner surface 130 has a radius of curvature 132 at cross-sectional line3-3. In that regard, the radius of curvature 132 is between about 5 mmand about 70 mm and, in some instances, between about 9.3 mm and about15.3 mm. In the present embodiment, the radius of curvature 132 isapproximately 12 mm. In a smaller embodiment, the radius of curvature132 is approximately 9.3 mm. In a larger embodiment, the radius ofcurvature is approximately 15.3 mm. In some instances, the radius ofcurvature 132 is smaller than the radius of curvature of the uppersurface 116. In the present embodiment, configured for use as a medialmeniscus replacement, the radius of curvature 132 may be considered alateral-anterior radius of curvature of the prosthetic device 100. In alateral meniscus replacement, the corresponding radius of curvature of asimilar prosthetic device configured for the lateral replacement may bewithin a similar range and be considered a medial-anterior radius ofcurvature of the prosthetic device.

At cross-sectional line 3-3, the bridge 114 generally extends at anangle 134 with respect to an axis 136 extending substantiallyperpendicular to a plane generally defined by the prosthetic device 100,as shown. In some instances, the axis 136 extends from the intersectionof the bridge 114 with the central body portion 110. The angle 134 isbetween about 20 degrees and about 70 degrees and, in some instances, isbetween about 30 degrees and about 32 degrees. In the presentembodiment, the angle 134 is approximately 31 degrees. In a smallerembodiment, the angle 134 is approximately 30 degrees. In a largerembodiment, the angle 134 is approximately 32 degrees. In the presentembodiment, configured for use as a medial meniscus replacement, theangle 134 may be considered a lateral-anterior angle of the prostheticdevice 100. In a lateral meniscus replacement, the corresponding angleof a similar prosthetic device configured for the lateral replacementmay be within a similar range and be considered a medial-anterior angleof the prosthetic device.

Referring more specifically to FIG. 4, shown therein is a diagrammaticcross-sectional view of the prosthetic device 100 taken along sectionline 4-4 of FIG. 2. As shown, the first portion 112 of the outer bodyportion 108 has a height or thickness 138 at cross-sectional line 4-4.In that regard, the height or thickness 138 of the first portion 112 isbetween about 4 mm and about 15 mm and, in some instances, is betweenabout 5.8 mm and about 9.5 mm. In the present embodiment, the height orthickness 138 of the first portion 112 is approximately 7.7 mm. In asmaller embodiment, the height or thickness 138 is approximately 5.8 mm.In a larger embodiment, the height or thickness 138 is approximately 9.5mm. In the present embodiment, configured for use as a medial meniscusreplacement, the height or thickness 138 may be considered a mid-medialheight or thickness of the first portion 112 of the outer body portion108. In a lateral meniscus replacement, the corresponding height orthickness of a similar prosthetic device configured for the lateralreplacement may be within a similar range and be considered amid-lateral height or thickness of the outer body portion.

Similarly, the bridge 114 of the outer body portion 108 has a height orthickness 140 at cross-sectional line 4-4. The height or thickness 140of the bridge 114 is also between about 4 mm and about 15 mm and, insome instances, is between about 4.6 mm and about 7.8 mm. In the presentembodiment, the height or thickness 140 of the bridge 114 isapproximately 6.0 mm. In a smaller embodiment, the height or thickness140 is approximately 4.6 mm. In a larger embodiment, the height orthickness 140 is approximately 7.8 mm. In the present embodiment,configured for use as a medial meniscus replacement, the height orthickness 140 may be considered a mid-lateral height or thickness of thebridge 114. In a lateral meniscus replacement, the corresponding heightor thickness of a similar prosthetic device configured for the lateralreplacement may be within a similar range and be considered a mid-medialheight or thickness of the bridge.

The inner surface 130 connecting the bridge 114 to the articulatingsurface 116 has a radius of curvature 142 at cross-sectional line 4-4.In that regard, the radius of curvature 142 is between about 8 mm andabout 30 mm and, in some instances, between about 8.9 mm and about 15.2mm. In the present embodiment, the radius of curvature 142 isapproximately 14 mm. In a smaller embodiment, the radius of curvature142 is approximately 8.9 mm. In a larger embodiment, the radius ofcurvature is approximately 15.2 mm. In some instances, the radius ofcurvature 142 is smaller than the radius of curvature of the uppersurface 116. In the present embodiment, configured for use as a medialmeniscus replacement, the radius of curvature 142 may be considered amid-lateral radius of curvature of the prosthetic device 100. In alateral meniscus replacement, the corresponding radius of curvature of asimilar prosthetic device configured for the lateral replacement may bewithin a similar range and be considered a mid-medial radius ofcurvature of the prosthetic device.

At cross-sectional line 4-4, the bridge 114 generally extends at anangle 144 with respect to an axis 146 extending substantiallyperpendicular to a plane generally defined by the prosthetic device 100,as shown. The angle 144 is between about 15 degrees and about 60 degreesand, in some instances, is between about 18 degrees and about 20degrees. In the present embodiment, the angle 144 is approximately 19degrees. In a smaller embodiment, the angle 144 is approximately 18degrees. In a larger embodiment, the angle 144 is approximately 20degrees. In the present embodiment, configured for use as a medialmeniscus replacement, the angle 144 may be considered a mid-lateralangle of the prosthetic device 100. In a lateral meniscus replacement,the corresponding angle of a similar prosthetic device configured forthe lateral replacement may be within a similar range and be considereda mid-medial angle of the prosthetic device.

The bridge 114 of the outer body portion 108 also has a width orthickness 148 at cross-sectional line 4-4. The width or thickness 148 ofthe bridge 114 is between about 1 mm and about 5 mm and, in someinstances, is between about 2.0 mm and about 3.3 mm. In the presentembodiment, the width or thickness 140 of the bridge 114 isapproximately 2.0 mm. In a smaller embodiment, the width or thickness140 is also approximately 2.0 mm. In a larger embodiment, the width orthickness 140 is approximately 3.3 mm. In the present embodiment,configured for use as a medial meniscus replacement, the width orthickness 148 may be considered a mid-lateral width or thickness of thebridge 100. In a lateral meniscus replacement, the corresponding widthor thickness of a similar prosthetic device configured for the lateralreplacement may be within a similar range and be considered a mid-medialwidth or thickness of the bridge. In some embodiments, the width orthickness of the bridge 114 is substantially constant along the lengthof the bridge from the anterior to the posterior of the prostheticdevice 100. In other embodiments, the width or thickness of the bridge114 varies along the length of the bridge from the anterior to theposterior of the prosthetic device 100.

Referring now to FIG. 5, shown therein is a diagrammatic cross-sectionalview of the prosthetic device 100 shown in comparison with analternative prosthetic device 102. More specifically, FIG. 5 is across-sectional view of the prosthetic device 100 taken along sectionline 4-4 of FIG. 2 shown in comparison to a cross-sectional view of thealternative prosthetic device 102 taken along a correspondingcross-section line. As illustrated, the prosthetic device 100 has areduced profile relative to the larger profile of the prosthetic device102. In that regard, the prosthetic device 102 is sized to substantiallymatch the size of a natural meniscus of the patient, whereas theprosthetic device 100 has a reduced size relative to the naturalmeniscus it is to replace. In that regard, the prosthetic device 100 ispretensioned to a reduced size in some instances. In one particularembodiment, the imbedded fibers positioned within the outer body portion108 are utilized to the pretension the device 100. In some embodiments,the prosthetic device 100 is configured to stretch or expand oncepositioned within the knee joint and subjected to load bearing. In someinstances, the outer body portion 108 is configured to expand outwardlyas loading forces are applied to the prosthetic device and the innerbody portion 110 is configured to conform to the engagement surfaces ofthe femur and tibia as the loading forces are applied. To that end, theangles of the inner walls of the prosthetic device 100 that will matewith the femur are steep enough such that as loading is applied to theprosthetic device the outer body portion 108 will be urged outward andnot simply compressed downward. Accordingly, in some instances theprosthetic device 100 selected for use in treating a patient isintentionally smaller in size than the natural meniscus it will bereplacing.

Referring to FIG. 6, shown therein is a diagrammatic cross-sectionalview of the prosthetic device 100 taken along section line 6-6 of FIG.2. As shown, the first portion 112 of the outer body portion 108 has aheight or thickness 150 at cross-sectional line 4-4. In that regard, theheight or thickness 150 of the first portion 112 is between about 4 mmand about 15 mm and, in some instances, is between about 5.8 mm andabout 9.1 mm. In the present embodiment, the height or thickness 150 ofthe first portion 112 is approximately 7.5 mm. In a smaller embodiment,the height or thickness 150 is approximately 5.8 mm. In a largerembodiment, the height or thickness 150 is approximately 9.1 mm. In thepresent embodiment, configured for use as a medial meniscus replacement,the height or thickness 150 may be considered a medial posterior heightor thickness of the first portion 112 of the outer body portion 108. Ina lateral meniscus replacement, the corresponding height or thickness ofa similar prosthetic device configured for the lateral replacement maybe within a similar range and be considered a lateral posterior heightor thickness of the outer body portion.

Similarly, the bridge 114 of the outer body portion 108 has a height orthickness 152 at cross-sectional line 6-6. The height or thickness 152of the bridge 114 is also between about 4 mm and about 15 mm and, insome instances, is between about 8 mm and about 12.1 mm. In the presentembodiment, the height or thickness 152 of the bridge 114 isapproximately 8.8 mm. In a smaller embodiment, the height or thickness152 is approximately 8.0 mm. In a larger embodiment, the height orthickness 152 is approximately 12.1 mm. In the present embodiment,configured for use as a medial meniscus replacement, the height orthickness 152 may be considered a lateral posterior height or thicknessof the bridge 114. In a lateral meniscus replacement, the correspondingheight or thickness of a similar prosthetic device configured for thelateral replacement may be within a similar range and be considered amedial posterior height or thickness of the bridge.

The inner surface 130 connecting the bridge 114 to the articulatingsurface 116 has a radius of curvature 154 at cross-sectional line 6-6.In that regard, the radius of curvature 154 is between about 5 mm andabout 50 mm and, in some instances, is between about 7.4 mm and about11.6 mm. In the present embodiment, the radius of curvature 154 isapproximately 11 mm. In a smaller embodiment, the radius of curvature154 is approximately 7.4 mm. In a larger embodiment, the radius ofcurvature 154 is approximately 11.6 mm. In some instances, the radius ofcurvature 154 is smaller than the radius of curvature of the uppersurface 116. In the present embodiment, configured for use as a medialmeniscus replacement, the radius of curvature 154 may be considered alateral posterior radius of curvature of the prosthetic device 100. In alateral meniscus replacement, the corresponding radius of curvature of asimilar prosthetic device configured for the lateral replacement may bewithin a similar range and be considered a medial posterior radius ofcurvature of the prosthetic device.

At cross-sectional line 6-6, the bridge 114 generally extends at anangle 156 with respect to an axis 158 extending substantiallyperpendicular to a plane generally defined by the prosthetic device 100,as shown. The angle 156 is between about 15 degrees and about 60 degreesand, in some instances, is between about 29 degrees and about 31degrees. In the present embodiment, the angle 156 is approximately 30degrees. In a smaller embodiment, the angle 156 is approximately 29degrees. In a larger embodiment, the angle 156 is approximately 31degrees. In the present embodiment, configured for use as a medialmeniscus replacement, the angle 156 may be considered a lateralposterior angle of the prosthetic device 100. In a lateral meniscusreplacement, the corresponding angle of a similar prosthetic deviceconfigured for the lateral replacement may be within a similar range andbe considered a medial posterior angle of the prosthetic device.

Referring to FIG. 7, shown therein is a diagrammatic cross-sectionalview of the prosthetic device 100 taken along section line 7-7 of FIG.2. Section line 7-7 extends through the bridge 114 of the outer bodyportion 108 of the prosthetic device 100. As shown, the bridge 114 ofthe outer body portion 108 has an anterior height or thickness 160 atcross-sectional line 7-7. In that regard, the anterior height orthickness 160 of the bridge 114 is between about 4 mm and about 15 mmand, in some instances, is between about 5.7 mm and about 9.3 mm. In thepresent embodiment, the anterior height or thickness 160 of the bridge114 is approximately 7.8 mm. IN a smaller embodiment, the anteriorheight or thickness 160 is approximately 5.7 mm. In a larger embodiment,the anterior height or thickness 160 is approximately 9.3 mm. The bridge114 of the outer body portion 108 has a posterior height or thickness162 at cross-sectional line 7-7. The posterior height or thickness 162of the bridge 114 is between about 4 mm and about 20 mm and, in someinstances, is between about 7.7 mm and about 12.7 mm. In the presentembodiment, the posterior height or thickness 162 of the bridge 114 isapproximately 9.0 mm. In a smaller embodiment, the posterior height orthickness 162 is approximately 7.7 mm. In a larger embodiment, theposterior height or thickness 162 is approximately 12.7 mm.

The anterior portion of the upper surface of the bridge 114 has ananterior radius of curvature 164 at cross-sectional line 7-7. In thatregard, the anterior radius of curvature 164 is between about 10 mm andabout 100 mm and, in some instances, is between about 23.0 mm and about33.1 mm. In the present embodiment, the radius of curvature 164 isapproximately 72 mm. In another embodiment, the radius of curvature 164is approximately 28 mm. In a smaller embodiment, the radius of curvature164 is approximately 23 mm. In a larger embodiment, the radius ofcurvature 164 is approximately 33.1 mm. The posterior portion of theupper surface of the bridge 114 has a posterior radius of curvature 166at cross-sectional line 7-7. In that regard, the posterior radius ofcurvature 166 is between about 5 mm and about 70 mm and, in someinstances, is between about 15.2 mm and about 24.2 mm. In the presentembodiment, the radius of curvature 166 is approximately 18.5 mm. In asmaller embodiment, the radius of curvature 166 is approximately 15.2mm. In a larger embodiment, the radius of curvature 166 is approximately24.2 mm.

Further, the anterior portion of the upper surface of the bridge 114generally extends at an anterior angle 168 with respect to an axis 170extending substantially perpendicular to a plane generally defined bythe prosthetic device 100, as shown. The anterior angle 168 is betweenabout 45 degrees and about 75 degrees and, in some instances, is betweenabout 62 degrees and about 68 degrees. In the present embodiment, theangle 168 is approximately 65 degrees. In a smaller embodiment, theangle 168 is approximately 62 degrees. In a larger embodiment, the angleis approximately 68 degrees. The posterior portion of the upper surfaceof the bridge 114 generally extends at an posterior angle 172 withrespect to an axis 174 extending substantially perpendicular to a planegenerally defined by the prosthetic device 100, as shown. The posteriorangle 172 is between about 35 degrees and about 70 degrees and, in someinstances, is between about 55 degrees and about 61 degrees. In thepresent embodiment, the angle 172 is approximately 58 degrees. In asmaller embodiment, the angle 172 is approximately 55 degrees. In alarger embodiment, the angle 172 is approximately 61 degrees.

The central body portion 110 has a height or thickness 176 between theupper articulation surface 116 and the lower articulation surface 118 atcross-sectional line 7-7. In some embodiments, the height or thickness176 is the minimal thickness of the central body portion 110 and, inmore specific embodiments, the minimal thickness of the entireprosthetic device 100. To that end, the height or thickness 176 isbetween about 1 mm and about 3 mm and, in some instances, is betweenabout 1.2 mm and about 2.1 mm. In the present embodiment, the height orthickness 176 is approximately 1.5 mm. In a smaller embodiment, theheight or thickness 176 is approximately 1.2 mm. In a larger embodiment,the height or thickness 176 is approximately 2.1 mm.

Referring again to FIG. 2, as shown therein the prosthetic device 100has a maximum or total width 178 extending between the outer boundariesof the first portion 112 and the bridge 114 of the outer body portion108. In that regard, the width 178 is between about 20 mm and about 65mm and, in some instances, is between about 24.8 mm and about 40.6 mm.In the current embodiment, the width 178 is approximately 32 mm. In asmaller embodiment, the width 178 is approximately 24.8 mm. In a largerembodiment, the width 178 is approximately 40.6 mm. Also, the prostheticdevice 100 has a maximum or total length 180 extending between theopposing outer boundaries of the first portion 112 of the outer bodyportion 108. In that regard, the length 180 is between about 20 mm andabout 60 mm and, in some instances, is between about 34.5 mm and about56.5 mm. In the current embodiment, the length 180 is approximately 46mm. In a smaller embodiment, the length 180 is approximately 34.5 mm. Ina larger embodiment, the length 180 is approximately 56.5 mm.

Referring now to FIG. 8, shown therein is a diagrammatic cross-sectionalview of the prosthetic device 100 shown in comparison with analternative prosthetic device 102. More specifically, FIG. 8 is across-sectional view of the prosthetic device 100 taken along sectionline 8-8 of FIG. 2 shown in comparison to a cross-sectional view of thealternative prosthetic device 102 taken along a correspondingcross-section line. Similar to FIG. 5 discussed above, the prostheticdevice 100 has a reduced profile relative to the larger profile of theprosthetic device 102. In that regard, the prosthetic device 102 isagain sized to substantially match the size of a natural meniscus of thepatient, whereas the prosthetic device 100 has a reduced size relativeto the natural meniscus it is to replace. The prosthetic device 100 ispretensioned to a reduced size in some instances. In some embodiments,the prosthetic device 100 is configured to stretch or expand oncepositioned within the knee joint and subjected to load bearing. In someinstances, the outer body portion 108 is configured to expand outwardlyas loading forces are applied to the prosthetic device and the innerbody portion 110 is configured to conform to the engagement surfaces ofthe femur and tibia as the loading forces are applied. To that end, theangles of the inner walls of the prosthetic device 100 that mate withthe femur are steep enough such that as loading is applied to theprosthetic device the outer body portion 108 will be urged outward andnot simply compressed downward. Accordingly, in some instances theprosthetic device 100 selected for use in treating a patient isintentionally smaller in size than the natural meniscus it replaces.

In some instances the outer body portion 108 has an increased stiffnessrelative to the central body portion 110. As discussed in greater detailbelow, this increased stiffness may be the result of different materialproperties, geometries, support features, and/or other mechanisms forvarying the stiffness between the central body portion 110 and the outerbody portion 108. Further, in some embodiments, the outer body portion108 is pre-tensioned to improve the mating fit of the prosthetic device100 within the knee joint. In some instances pre-tensioning theprosthetic device 100 maximizes the contact area of the load-bearingsurfaces of the prosthetic device 100 to distribute loading through theprosthetic device 100 in a manner substantially similar to that of ahealthy natural meniscus. In some embodiments, a single feature of theouter body portion 108 is utilized to both pretension the prostheticdevice 100 and also increase the stiffness and/or strength of outer bodyportion.

In some embodiments the outer body portion 108 of the prosthetic device100 includes a deformation control element to limit the deformation ofthe outer body portion. In some embodiments, the deformation controlelement is also utilized to pretension the device as discussed above.The deformation control element may be a material property, a structuralproperty, an additional component, and/or combinations thereof. Itshould be noted that the various deformation control elements describedherein may be combined to further limit or define the amount ofdeformation of the outer body portion 108 and/or tailor the amount ofpretensioning of the prosthetic device. In some embodiments, the outerbody portion 108 is includes materials or fibers for increasing thestiffness and/or strength of the outer body portion relative to thecentral body portion 110. In one specific embodiment, the central bodyportion 110 of the prosthetic device 100 is formed of Bionate 80A withthe outer body portion 108 reinforced with DSM Dyneema UHMWPE fibers.Bionate 80A is a resilient polymeric material having a modulus ofelasticity similar to that of articular cartilage and, in someinstances, between about 1-10 MPa and, in some instances, between about4-8 MPa. As another example, in one embodiment the outer body portion108 includes carbon fibers providing additional strength and limitingthe flexibility of the outer body portion. In some embodiments thecarbon fibers are injected prior to the curing of the outer body portion108. In other embodiments, the outer body portion 108 is formed ormolded around the carbon fibers. In other embodiments, other additivesor fibers are utilized to reinforce the material of the outer bodyportion 108. The particular additives or reinforced materials that areused depend upon the based material(s) used for forming the outer bodyportion 108 and the prosthetic device 100. In some instances theadditives are distributed substantially uniformly through the basematerial(s) of the outer body portion 108. In other embodiments thedeformation control element comprises only a defined portion of theouter body portion 108. In that regard, the deformation control elementmay extend along only a portion of the outer body portion 108, thedeformation control element may be positioned within a particularportion of the outer body portion, and/or combinations thereof.

In other embodiments, the outer body portion 108 has a reinforcing layerthat serves as the deformation control element and/or the pretensioningelement. In some instances, the reinforcing layer includes a wire,cable, filament, thread, and/or structure extending therethrough Thereinforcing layer increases the stiffness of the outer body portion 108to limit the flexibility, deformity, and/or tensions the prostheticdevice 100. In some embodiments, the reinforcing layer comprises acarbon fiber. In other embodiments, the reinforcing layer comprises ametal, polymer, or other material having an increased hardness and/orstiffness relative to the material comprising the central body portion110. In some embodiments, at least a portion of the outer body portion108 is formed around the reinforcing layer. In other embodiments, thereinforcing layer is inserted into the outer body portion 108 prior tocuring of the prosthetic device 108. In some embodiments, thereinforcing layer is inserted into an opening in the body portion 108and then additional material is inserted into the opening to close theopening and secure the reinforcing layer therein. The reinforcing layerhas a cross-sectional profile configured to provide the desiredstiffness, deformation properties, and/or tension to the outer bodyportion 108. Further the reinforcing layer is positioned within theouter body portion 108 appropriately to provide the desired stiffness,deformation properties, and/or tension to the outer body portion. Insome embodiments, the outer body portion 108 includes multiplereinforcing layers therein. In that regard, the multiple reinforcinglayers may be spaced equally about the outer body portion 108 and/orgrouped into specific areas of the outer body portion. In someinstances, the multiple reinforcing layers form a circumferentialreinforcing wall extending from adjacent an upper surface of theprosthetic device to adjacent a lower surface of the prosthetic device.

In some embodiments, the outer body portion 108 includes one or morerecesses and/or undercuts for receiving a component for defining thedeformation properties of the outer body portion. For example, in someinstances the component may be a wire, cable, or filament similar tothose described above. In other instances, the component may be amaterial that is injected or otherwise introduced into the recess in theouter body portion 108. Generally, the size of the recess and theproperties of the component are tailored to achieve the desireddeformation properties and/or tensioning of the outer body portion 108.In some embodiments, the recess comprises between ⅛ and ⅔ of the heightof the outer body portion 108 and between ⅛ and ⅔ of the width of theouter body portion. In many embodiments, the component substantiallyfills the entire recess 44. However, in some embodiments the componentis sized such that it fills only a portion of the recess. In suchembodiments, the remaining portion of the recess may remain vacant or befilled with another material. In some embodiments, the component issecured in the recess by the introduction of additional material intothe open space remaining in the recess.

As noted above, the prosthetic device 100 is configured for use withoutbeing fixedly secured to the femur or tibia. However, in someembodiments the prosthetic device 100 includes a fixation member forengaging a portion of bone or surrounding tissue. In some suchembodiments, the prosthetic device 100 includes fixation memberextending down from the lower surface of the prosthetic device. Thefixation member extends from the lower surface adjacent to andsubstantially parallel to the bridge 114 in some instances. In oneembodiment, the fixation member comprises a keel structure configured toengage a complementary keyhole shaped groove that has been surgicallyincised in a portion of the tibia, such as the tibia plateau, accordingto a keyhole surgical approach. In another embodiment, the fixationmember comprises a dovetail configured to engage a dovetailed grooveprepared in the tibia. In other embodiments, the fixation member extendsfrom other portions of the prosthetic device and/or in other directions,including directions substantially perpendicular to the bridge 114and/or oblique to the bridge 114. Alternative positioning andorientations of the fixation member are used to accommodate alternativesurgical approaches, patient specific anatomical attributes, meniscusspecific orientations, physician preference, and/or other factors. Thefixation member is manufactured as an integral part of the prostheticdevice in some embodiments.

In some embodiments, a fixation device (e.g., bone screw, nail, staple,etc.) is utilized in combination with or in lieu of the fixation memberto secure the prosthetic device 10 to the tibia. In that regard, theprosthetic device includes an opening or recess configured to receiveand mate with the fixation device in some embodiments. Further still, insuch embodiments where fixation is desired the bottom surface of theprosthetic device is coated with a bioactive coating to encourage thein-growth of natural tissue to further improve fixation of theprosthetic device to the tibial plateau in some instances. The coatingis formed by grit blasting or spraying the bottom surface with anysuitable material for encouraging tissue growth and, in some embodiment,is specifically adapted for promoting bone growth between the tibia andthe prosthetic device.

In some instances, applying an internal pre-tension to the prostheticdevice 100 maximizes the contact area of the upper and lower surfaces116, 118 and distributes the loading in an optimal way, simulating theload distribution of a natural meniscus. Based on experimental andcomputational (e.g., finite element) analyses, it was found thatapplying an internal pretension to a meniscus prosthetic device such asprosthetic device 100 described above improves the device'sfunctionality in terms of load bearing. In particular, pretensioningreduces the peak stresses applied on articular cartilage, increases thetotal load bearing threshold of the device, and improves the loaddistribution of the device.

In some embodiments the prosthetic device 100 comprises a pliable hostmaterial—such as PTG Bionate® Polycarbonate-Urethane (PCU), 80 ShoreA—integrated with imbedded fibers—such as DSM Dyneema® fibers. In suchembodiments, the imbedded fibers may be utilized to pretension theprosthetic device. Where the prosthetic device 100 has beenpretensioned, the pliable host material gives the prosthetic device theability to conform to the engaging surfaces of the femur and tibia as afunction of load. On the other hand, the imbedded fibers bear more ofthe load than the pliable host material such that the risk forshort-term failure of the prosthetic device is significantly decreased.In some instances, pretensioning is applied to a prosthetic device 100that is smaller than the natural meniscus being replaced. In thatregard, previous mechanical tests as well as finite element analyseshave shown that pretensioning is effective when using a scaled-downimplant. In some embodiments, the prosthetic device 100 subjected topretensioning is scaled-down by 0.5 to 7.5% relative to the size of thenatural meniscus being replaced and, in some instances, is scaled-downbetween about 2.0% and about 4.0%. In that regard, the specific size ofthe prosthetic device may be determined based on a specific candidatepatient's knee structure. In some instances, the pretensioning of thedevice itself results in the reduced size of the device. Specifically,the tension of the fibers or other elements that tension the devicecause the prosthetic device to contract or shrink in overall size. Inother instances, the pretensioning of the device does not affect thesize of the device. In some instances, upon loading within the kneejoint the prosthetic device is expanded or stretched to a desiredimplantation size.

Add Contact Zones

In the pretensioned devices, contact between the prosthetic device 100and the femur is reached initially at the outer body portion 108. whichcauses the central body portion 110 of the prosthetic device to bestretched as the weight is transferred through the femur to theprosthetic device and urges the outer body portion 108 outward. Theengagement angles of the outer body portion 108 are such thatcompression forces applied to the device 100 are transferred at leastpartially to the reinforcing fibers. In some instances, the outer bodyportion 108 is urged outwardly and the central body portion 110stretches upon weight being applied through the femur, rather than thefemur simply compressing the outer body portion. This stretching of thecentral body portion 110 and the upper and lower articulation surfaces116, 118 increases the contact area between the prosthetic device andthe femur and tibia (see transition between FIGS. 9 b and 10, forexample) as well as lowers the average and peak loading stresses actingon the prosthetic device 100.

As shown in FIG. 9 a, in some instances the reinforcing fibers 124limit, restrict, or otherwise oppose outward movement or deformation ofthe outer body portion 108, but allow inward folding or collapsing ofthe device 100. The prosthetic device 100 is shown in a foldedimplantation orientation in FIG. 9 a. In that regard, the bridge portion114 is folded or collapsed towards the central body portion 110 tofacilitate introduction of the device 100 into the knee joint. In someembodiments, the bridge 114 is both folded and compressed in thisinsertion configuration. In some instances, the bridge 114 is resilientsuch that it returns to its original, unfolded configuration afterinsertion (see FIG. 9 b for example). In particular, once the bridge 114reaches the other side of the femur 104 and has room to expand, itreturns to its neutral position. Accordingly, in some surgicalprocedures a portion of the prosthetic device 100 is folded and/orcompressed to facilitate insertion of the device into the knee joint.While the bridge 114 is illustrated as being folded/compressed in thepresent embodiment, in other instances other portions of the outer bodyportion 108 are folded and/or compressed.

As shown in FIG. 9 b, upon initial contact between the femur and thetibia with the prosthetic device 100 there are gaps 182 between theupper surface 116 and the femur and gaps 184 between the lower surface118 the tibia. In this regard, the initial contact of the bones 104, 106and the prosthetic device 100 is with an upper constant contact area 186and a lower constant contact area 188. The constant contact areas 186and 188 are in constant contact with the femur and tibia, respectively,after insertion of the prosthetic device 100 into the knee joint.Accordingly, in some instances the constant contact areas 186 and 188comprise an annular surface areas of the upper and lower portions of thedevice 100. In that regard, the constant contact areas 186 and 188 maycomprise part of the outer body portion 108 or a combination of theouter body portion 108 and the central body portion 110. Within theupper and lower constant contact areas 186, 188 are upper and lowerintermittent contact areas 190 and 192, respectively. The intermittentcontact areas 190, 192 come into contact with the femur and tibia,respectively, upon sufficient loading of the prosthetic device 100. Morespecifically, as load is applied to the prosthetic device 100 thetapered surfaces of the constant contact areas 186, 188 urge the outerbody portion 108 slightly outwardly such that the femur and tibia comeinto contact with the intermittent contact areas 190, 192. In someinstances the pliable nature of the prosthetic devices material allowsthe intermittent contact areas 190, 192 to conform to the shape of thebearing condyles of the femur and tibia upon loading. In this manner,the intermittent contact areas 190, 192 do not constantly engage thefemur and tibia as the constant contact areas 186, 188 do. In someinstances, the intermittent contact areas 190, 192 are circumferentiallyor annularly bounded and/or defined by the constant contact areas 186,188, respectively. Further, in some embodiments, additional intermittentcontact areas 190, 192 are included outside of the constant contactareas 186, 188. Thus, in some instances, the intermittent contact areas190, 192 comprise part of the central body portion 110 and/or outer bodyportion 108. In some embodiments, the constant contact areas 186, 188extend to the perimeter of the device 100 such that the intermittentcontact areas are solely within the constant contact areas. In someinstances, the constant contact areas 186, 188 are shaped tosubstantially match a contour of the femur and/or tibia. Referring toFIG. 1, shown therein is one example of an orientation of an upperconstant contact area 186 and an intermittent contact area 190.

Referring to FIG. 10, as the prosthetic device 100 is subjected toweight bearing between the femur and tibia, the outer body portion isurged outwardly and the central body portion 110 stretches to achievethe substantially uniform contact between the upper and lower surfaces116, 118 and the femur and tibia. As shown, the gaps 182, 184 areeliminated and the intermittent contact areas 190,192 as well as theconstant contact areas 186, 188 are in contact with the femur and tibia,respectively. The pliability of the material of the central body portion110 facilitates the continuous contact as the material is able toconform to the shape of the engaging surfaces of the femur and tibia,which comprise cartilage in some instances. Further, the stretching andmating of the prosthetic device 100 reduces the translation and rotationof the prosthetic device within the knee joint. The reduced translationand rotation of the prosthetic device serves to limit wear damage to thecruciate ligaments over time.

Prosthetic Device Selection

In some embodiments, a prosthetic device is selected for a patient froma finite library or catalog of available prosthetic device. In thatregard, the available prosthetic devices are of various sizes, variousmaterials, and/or various shapes. In some instances, a selectionmethodology is applied to identify one or more suitable prostheticdevices and/or a best prosthetic device for a patient based on thepatient's anatomical features. In other instances, a custom prostheticdevice is designed and manufactured specifically for the patient basedon the patient's anatomical features. Specific methods for identifyingan appropriate prosthetic device for a patient will now be described. Itis recognized that the methods described herein may be usedindividually, combined with one another, and/or combined with othermethods in an effort to identify a suitable prosthetic device for thepatient.

In most healthy patient knees, the natural meniscus and the surroundingbone structures have substantially matching geometrical contours.Accordingly, in order to restore the function of the knee joint with aprosthetic meniscus, the prosthetic device should be configured tosubstantially match the geometrical contours of the surrounding bonestructures of the knee joint after implantation. Thus, in someembodiments the geometrical attributes of the patient's knee joints andthe prosthetic device are taken in consideration. In that regard, theboth the patient's healthy knee and the patient's damaged knee areconsidered, including the bone structures, the articular cartilage,and/or the menisci.

Referring now to FIG. 11, shown therein is a method 200 for identifyingat least one suitable prosthetic device for a patient. The method 200includes a pre-implantation matching process at step 202 and aduring-implantation matching process at step 204. The pre-implantationand during-implantation matching procedures 202 and 204 described hereinare utilized for both medial and lateral meniscus replacements in boththe left and right knees. The method 200 begins at step 202 with thepre-implantation matching process. The pre-implantation matching processof step 202 is comprised of one or more matching methods. Referring morespecifically to FIG. 12, in the present embodiment the pre-implantationmatching process 202 comprises three different matching methods: adirect geometrical matching method 206, a correlation parameters-basedmatching method 208, and a finite element-based matching method 210.Each of these three matching processes 206, 208, and 210 will bedescribed in greater detail below. While these processes 206, 208, and210 are described as being used together, in some instances only one ortwo of the three methods are utilized in the pre-implantation matchingprocess 202. In other instances, the processes 206, 208, and 210 areutilized in combination with additional and/or alternative matchingprocesses.

The direct geometrical matching process 206 begins at step 212 where CTand/or MRI scans of the healthy knee of a candidate patient areobtained. In some instances, the CT and/or MRI scans of the healthy kneeare utilized to identify the appropriate for measurements the prostheticdevice for the damaged knee. At step 214, the healthy knee joint issegmented into its various components. In some embodiments,image-processing algorithms are utilized to segment the knee joint. Insome embodiments, one or more of the bone surfaces, the articularcartilage, and the meniscus of the knee joint are segmented. Forexample, referring to FIG. 13, shown therein is a diagrammatic side viewof a patient's right knee joint 250 where the bone surfaces 252 andarticular cartilage 254 of the femur 256 and the tibia 258 have beensegmented. Further, the medial meniscus 260 extending between thearticular cartilage 254 has been segmented. In some instances, the bonesurfaces, the articular cartilage, and the meniscus are segmented inseparate steps. In other instances, the segmentation of the bonesurfaces, the articular cartilage, and the meniscus are performedapproximately simultaneously. In some embodiments, the internal kneejoint cavity is characterized based on the surfaces of the articularcartilage. In some instances, the healthy meniscus is defined at leastpartially based on the knee joint cavity defined by the articularcartilage. In some embodiments, at step 214 or a subsequent step of thedirect geometrical matching process 206, a virtual solid model 262 ofthe healthy meniscus 260 is built graphically, as shown in FIG. 14. Insome embodiments, the virtual solid model 262 is created in astereolithography (“STL”) format. The virtual model 262 is used in someinstances to compare the healthy meniscus 260 to the availableprosthetic devices.

In the present embodiment, at step 216, the segmented healthy meniscusis compared to available prosthetic devices. In some instances, thiscomparison includes comparing the relative sizes and shapes in terms oflinear dimensions (such as depths, widths, heights, and/or radii ofcurvature) in the different sections or regions of the meniscus; outersurfaces (such as upper and lower contact surfaces and/or peripheralsurfaces); and volumes. In some embodiments, each prosthetic device isgiven a score or ranking based on how well it matches each of thevarious dimensions of the natural meniscus. By combining the scores foreach of the dimensions, an overall score is obtained for each availableprosthetic device. In that regard, it is understood that the variousdimensions are weighted in some embodiments to emphasize the importanceof certain dimensions. The importance or weighting of the variousdimensions are determined by such factors as the patient's age, activitylevel, weight, and/or other factors considered by the treating medicalpersonnel. In some instances, the weighting function is determined by acomputer system based on the answers provided to prompted questions. Inother instances, the treating medical personnel manually set theweighting function of the various dimensions.

In that regard, it is understood that the best prosthetic device or aprosthetic device that will obtain the best score for a particulardimension is not necessarily one with the exact same measurements as thenatural meniscus. Rather, in some embodiments of the present disclosurethe prosthetic device is approximately the same size or smaller than anatural healthy meniscus. In some embodiments the prosthetic device isgenerally between about 5% and about 20% smaller than the naturalmeniscus in its relaxed pre-implantation state. Similarly, in someembodiments of the present disclosure the prosthetic device does notmatch the shape of the natural meniscus. For example, FIG. 22 is adiagrammatic perspective view of a prosthetic device 244 for use inreplacing a damaged natural meniscus according to the present disclosureshown in comparison to the dimensions of a healthy natural meniscus 246.As illustrated, the prosthetic device 244 does not match the dimensionsof the natural meniscus 246. In some embodiments, the best prostheticdevice is substantially the same size and shape as the natural meniscus.At step 218, one or more of the best-graded prosthetic devices isselected for the direct geometrical matching method as a suitableimplant for the specific candidate knee. In some embodiments, only asingle, best prosthetic device is identified by the geometrical matchingprocess 206 at step 218. In other embodiments, all of the availableprosthetic devices are ranked based on their score as calculated usingthe geometrical matching process 206. In yet other embodiments, all ofthe prosthetic devices suitable for the candidate knee are identifiedand the prosthetic devices that are not suitable are discarded aspotential implant options.

While the measurements and comparisons of the patient's knee andmeniscus have been described as being performed substantially byelectronic or automated means, in some embodiments the measurements aretaken manually, directed form CT/MRI scans. Further, these manualmeasurements may be compared with prosthetic device measurements. Theprosthetic device measurements are provided by the manufacturer in someinstances. In other instances, the measurements of the prosthetic deviceare obtained manually as well. The manual measurements may be utilizedto confirm the measurements and comparisons obtained using the imageprocessing algorithm and matching process or in lieu of the imageprocessing algorithm and matching process. Further, while the presentdisclosure discusses the use of CT and/or MRI scans, it is fullycontemplated that other medical imaging methods may be utilized.Accordingly, it is fully contemplated that alternative medical imagingdevices and methods may be utilized with any and all of the methodsdescribed herein.

The correlation parameters-based matching process 208 is utilized insome embodiments. The correlation parameters-based matching processutilizes dimension measurements based on one or more large-scale studiesof patients having healthy knees. Generally, the studies considered thedimensions of the patients' knees and defined “normal” or acceptableranges. In some instances, geometrical relationships or formulas basedon the measured dimensions of the bones and the menisci were calculatedfor each healthy subject. These geometrical relationships or formulasdefine the correlation parameters utilized for selecting an appropriateprosthetic device in some embodiments of the present disclosure.

Referring now to FIG. 15, shown therein is a chart setting forth variouscorrelation parameters according to one aspect of the presentdisclosure. In the present embodiment, five correlation parameters areidentified: area, width, length, perimeter, and coronal relation. Inother embodiments, a greater or fewer number of correlation parametersare utilized. Each of the correlation parameters is defined by formulaor equation comprised of dimensional measurements of the knee joint.These measurements are based on CT and MRI scans of the healthy subjectpatients of the large-scale studies in some instances. The areacorrelation parameter is defined by the meniscus contact area divided bythe tibia medial area, or

$A = {\frac{MA}{TMA}.}$The width correlation parameter is defined by the average meniscus widthdivided by the medial tibia width, or

${W = \frac{M\; W_{avg}}{TMW}},$where the average meniscus width is the average of the anterior meniscuswidth and posterior meniscus width, or

${M\; W_{avg}} = {\frac{{M\; W_{A}} + {M\; W_{P}}}{2}.}$The length correlation parameter is defined by the medial meniscuslength divided by the tibia medial length, or

$L = {\frac{MML}{TML}.}$The perimeter correlation parameter is defined by the meniscus perimeterdivided by the tibia medial perimeter, or

$P = {\frac{MP}{TMP}.}$The coronal relation correlation parameter is defined by the meniscuscoronal width divided by the tibia coronal width, or

$C = {\frac{M\; W_{C}}{TCW}.}$

The mean and standard deviation are calculated for each correlationparameter in the large scale studies. The means and standard deviationsare considered as the knee normative data or acceptable ranges.According to one large scale study, the normative data ranges were asfollows. The average coronal tibia width was 75.6 mm with a standarddeviation of 6.7 mm or 8.8%. The average meniscus width as measured inthe coronal plane was 32.1 mm with a standard deviation of 3.1 mm or9.6%. The average tibia medial length was 48.8 mm with a standarddeviation of 5.2 mm or 10.6%. The average tibia area was 1282.8 mm witha standard deviation of 227.2 or 17.7%. The average tibia medialperimeter was 92.9 mm with a standard deviation of 9. mm or 10.4%. Theaverage anterior meniscus width was 28.7 with a standard deviation of10.3 mm or 35.8%. The average posterior meniscus width was 28.7 mm witha standard deviation of 10.4 mm or 36.3%. The average medial meniscusbody width was 6.7 mm with a standard deviation of 11.7 mm or 173.3%.The average medial meniscus length was 44.5 mm with a standard deviationof 9.5 or 21.3%. The average meniscus perimeter was 87.6 mm with astandard deviation of 9.5 mm or 10.8%. The average anterior meniscusheight was 6.9 mm with a standard deviation of 11.7 mm or 169.6%. Theaverage posterior meniscus height was 7.4 mm with a standard deviationof 11.6 mm or 157.4%. The average medial meniscus height was 6.9 mm witha standard deviation of 11.6 mm or 167.2%. The average meniscus ovalarea was 965.68 mm with a standard deviation of 186.64 mm or 19.3%.

Based on these normative data ranges, the following correlationparameter ranges were determined. The average area correlation parameterwas 0.75 with a standard deviation of 0.08 or 10.77%. The averageperimeter correlation parameter was 0.95 with a standard deviation of0.05 or 5.0%. The average width correlation parameter was 0.87 with astandard deviation of 0.06 or 6.6%. The average length correlationparameter was 0.91 with a standard deviation of 0.07 or 8.0%. Theaverage coronal relation correlation parameter was 0.37 with a standarddeviation of 0.03 or 7.1%. It is contemplated that additionallarge-scale studies may be performed in the future and that the acceptedranges for the correlation parameters discussed herein below may beadjusted as necessary to conform with the accepted dimensional ranges inthe field.

Referring now to FIGS. 16-19, shown therein are various views of a kneejoint 280 based on MRI and/or CT scans identifying measurements of theanatomical features of the knee joint. For example, referring morespecifically to FIG. 16, a cross-sectional top view of the knee joint280 identifying various measurements of the anatomical features isprovided. In particular, the width of the meniscus as measured in thecoronal plane (labeled MW) and the coronal tibia width (labeled TPW) areidentified. These parameters are utilized for calculating the coronalrelation as described above. Further, the tibia medial length (labeledML) is identified along with the tibia medial perimeter (labeled TMP).Referring more specifically to FIG. 17, a cross-sectional top view ofthe knee joint 280 similar to that of FIG. 16, but identifyingmeasurements of other anatomical features is provided. Specifically, theanterior and posterior meniscus widths (labeled MWA and MWP,respectively) are provided. Also, the medial meniscus length (labeledMML) and the meniscus perimeter (labeled P) are provided. Finally, themedial meniscus body width (labeled MMBW) is provided. Referring to FIG.18, a cross-sectional sagittal view close-up of the knee joint 280identifying the medial meniscus height (labeled Hcross) is provided.Finally, referring to FIG. 19, a cross-sectional side view close-up ofthe knee joint 280 identifying anterior and posterior meniscus heights(labeled HA and HP, respectively) is provided. It is fully contemplatedthat additional and/or alternative views of the knee joint 280 beprovided. In addition, it is fully contemplated that additional and/oralternative measurements of the knee joint 280 be provided.

The correlation parameters-based matching process 208 begins at step 220where CT and/or MRI scans of the injured knee of a candidate patient areobtained. Based on the imaging of the injured knee, various anatomicalmeasurements of the knee can be obtained. For example, in some instancesit is desirable to obtain information regarding the dimensions of thetibia. In that regard, the dimensions of the tibia discussed above withrespect to the correlation parameters (e.g., tibia medial area, tibiamedial width, tibia medial length, tibia medial perimeter, tibia coronalwidth, and/or other tibia dimensions) are obtained in some instances.

The process 208 continues at step 222 where the correlation parametersfor one or more of the available prosthetic devices are determined. Thegeometrical relationship formulas of the correlation parameters arecalculated for the prosthetic device based on the available candidateknee data and compared to the accepted normative data for eachprosthetic device. Each prosthetic device is given a sub-grade for eachcorrelation parameter based on how well the device matches up with theaccepted ranges for that correlation parameters. In that regard, anacceptable range of values for the prosthetic device can be determinedbased the available measurements of the candidate knee and the normativedata (e.g., normative range ±standard deviation) for the candidate knee.For example, with respect to the area correlation parameter, theacceptable range of meniscus contact areas for the prosthetic devicescan be determined by multiplying the normative range of acceptable areasby the tibia medial area, or A×TMA=MA. The acceptable ranges for otheraspects of the prosthetic device may be calculated similarly for each ofthe correlation parameters.

The process 208 continues at step 224 where the calculated correlationparameters are compared to the normative or accepted correlationparameters. Depending on how well the prosthetic device fits within therange for each correlation parameter, a sub-grade is determined for thatparameter. The better the fit, the better the sub-grade for thatparameter. In some instances, the grades are binary. Meaning if thedevice is within the acceptable range it receives the best score and ifthe device is outside of the range it receives the worst score. Similarto the previous geometrical matching method, the best-graded prostheticdevice is calculated by adding up all of the sub-grades to determine anoverall grade. In that regard, it is understood that the variouscorrelation parameters are weighted in some embodiments to emphasize theimportance of certain correlation parameters. The importance orweighting of the correlation parameters are determined by such factorsas the patient's age, activity level, weight, and/or other factorsconsidered by the treating medical personnel. In some instances, theweighting function for the correlation parameters is determined by acomputer system based on the answers provided to prompted questions. Inother instances, the treating medical personnel manually set theweighting function for the correlation parameters.

Further, it is understood that the correlation parameters may varydepending on the type of implant being considered. For example, in someembodiments of the present disclosure the prosthetic devices aredesigned to be between about 5% and about 20% smaller than the naturalmeniscus in its relaxed pre-implantation state. Accordingly, such sizingcan be taken into consideration when determining the acceptable rangesof the dimensions for the prosthetic device as they relate to thecorrelation parameters. At step 226, one or more of the best-gradedprosthetic devices is selected for the correlation parameters-basedmatching process 208 as a suitable implant for the specific candidateknee. In some embodiments, only a single, best prosthetic device isidentified by the correlation parameters-based matching process 208. Inother embodiments, all of the available prosthetic devices are rankedbased on their score as calculated using the correlationparameters-based matching process 208. In yet other embodiments, all ofthe prosthetic devices suitable for the candidate knee are identifiedand the prosthetic devices that are not suitable are discarded aspotential implant options.

The finite element-based matching process 210 is utilized in someembodiments. The finite element-based matching process 210 begins atstep 228 where CT and/or MRI scans of the injured knee of a candidatepatient are obtained. In some instances, the same CT and/or MRI scansare utilized for both the finite element-based matching process 210 andthe correlation parameters-based matching 208. Similar to the directgeometrical matching process 206 discussed above with respect to thehealthy knee joint, at step 230 the injured knee joint of the patient issegmented into its various components, such as the bone, articularcartilage, and menisci. In some instances, a three-dimensional solidgeometry model of the bones, cartilage, and menisci of the injured kneeis built. Based on the solid geometry, a patient-specific finite elementmodel of the knee is created at step 232. The patient-specific finiteelement model is configured to interface with various finite elementmodels of prosthetic devices in some instances. In that regard, in someembodiments the finite element model does not include the naturalmeniscus. Further, in some instances a finite element model of thepatient's healthy knee is created for use in evaluating theeffectiveness of the prosthetic devices in the injured knee.

The finite element-based matching process 210 continues at step 234where several simulation cases using the finite element model aretested. First, in some embodiments a load of up to 3-times the patient'sbody-weight is applied by the femur on the natural, damaged meniscus. Inother embodiments, the simulation of loading on the damaged meniscus isomitted. In other embodiments, a simulation of loading of the naturalmeniscus of the patient's healthy knee is performed and utilized as abase line. Regardless of whether a damaged or healthy meniscus isutilized, peak and average pressure measurements across the meniscus,peak and average pressure measurements acting on the femoral and tibialarticular cartilage, pressure distributions across the tibialis plateau,and/or other measurements are calculated.

Step 234 also includes testing one or more available prosthetic devicesunder a simulated load. Referring to FIG. 20, shown therein is athree-dimensional finite element model 290 of a knee joint 292 with aprosthetic device 294 positioned between a tibialis plateau 296 and afemur 298 according to one aspect of the present disclosure. For each ofthe available prosthetic devices, peak and average pressure measurementsacross the prosthetic device, peak and average pressure measurementsacting on the femoral and tibial articular cartilage, pressuredistributions across the tibialis plateau, and/or other measurements arecalculated. Referring to FIG. 21, shown therein is a simulated contactpressure map 300 for the prosthetic device 294 of FIG. 20 illustratingcontact pressures between the prosthetic device and the tibialis plateau296.

At step 236, the resultant pressure measurements for each of theprosthetic devices are compared to industrial accepted values and/or thenatural, healthy meniscus to provide the prosthetic devices withsub-grades for each of the measurements. For example, the peak pressuremeasurements of each of the prosthetic devices are compared to theaccepted ranges or the peak pressure measurements of the natural,healthy meniscus. The extent to which the prosthetic device is withinthe accepted range determines the device's sub-grade for peak pressure.Similarly, the peak and average pressure acting on the articularcartilages are compared to the allowed natural values for eachprosthetic device and the prosthetic device is given sub-gradesaccordingly. Further, the tibialis plateau pressure distributions foreach prosthetic device are compared to those of a healthy naturalmeniscus in terms of contact area size and stress concentrations. In oneparticular embodiment, a prosthetic device is given a perfect sub-gradescore if the resultant pressure distribution across the tibialis plateauis within ±15% of a healthy natural meniscus.

By combining the scores for each factor of the loading simulations, anoverall score is obtained for each available prosthetic device. In thatregard, it is understood that the various factors or measurements areweighted in some embodiments to emphasize the importance of certainaspects of the prosthetic device. The importance or weighting of thevarious factors are determined by such factors as the patient's age,activity level, weight, and/or other factors considered by the treatingmedical personnel. In some instances, the weighting function isdetermined by a computer system based on the answers provided toprompted questions. In other instances, the treating medical personnelmanually set the weighting function of the various dimensions.

In some instances, the finite element-based matching process 210includes motion simulations in addition to or in lieu of the loadbearing simulations discussed above. In that regard, the motion of theknee joint is compared to that of natural, healthy meniscus for one ormore available prosthetic devices. In some instances, these simulationsare designed to simulate typical patient movements such as walking,running, riding a bicycle, standing up, sitting down, etc. Theprosthetic devices are then provided sub-grades based on theirperformance for various factors related to knee movement (e.g., positionand/or loading support at various degrees of flexion). In someembodiments, the loading simulations and motion simulations are combinedsuch that the devices are scored base on loading functions during themotion simulations.

In some instances, the finite element-based matching process is comparedto a generic model rather than a patient specific model. For example, insome embodiments a plurality of finite element models are providedcorresponding to variety of different knee sizes and/or knee types. Aspecific finite element model from the plurality of different finiteelement models is selected for the current patient. In some embodiments,the specific finite element model is based at least partially on theknee size of the current patient. In one instance, the selected model isdetermined based on MRI data of the patient. Further, in some instancesthe selection of the specific finite element model is at least partiallybased on correlation parameters—such as those discussed above withrespect to the correlation-based matching process 208—for the candidateknee. In some instances, each of the available prosthetic devices istested or simulated with respect to each of the finite element modelsand the functionality of each the prosthetic devices is compared to theaccepted values for a natural, healthy meniscus. Accordingly, for eachof the finite models one or more suitable prosthetic devices areidentified. Thus, using only the associated bone measurements from theCT and/or MRI scans of a candidate knee, a best-matched finite elementmodel is identified and, from the best-matched finite element model, thecorresponding suitable prosthetic devices are identified as suitabledevices for the current patient.

In some embodiments, the pre-implantation matching method 202 continuesat step 240 by weighting the answers provided by the direct geometricalmatching process 206, the correlation parameters-based matching process208, and the finite element-based matching process 210. In someembodiments, each of the matching processes 206, 208, and 210 are givenequal weight. However, in other embodiments the matching processes 206,208, and 210 are given unequal weights. For example, where a genericfinite element model has been utilized-rather than a patient-specificgenerated finite element model-the finite element model-basedcorrelation may be given less weight than the direct geometricalmatching process 206 and the correlation parameters-based matchingprocess 208. The determination of the weighting of the differentmatching processes 206, 208, and 210 is determined by the treatingmedical personnel in some instances. Finally, the pre-implantationmatching method 202 continues at step 242 with the identification of oneor more suitable prosthetic devices are identified. In some embodiments,a single “best” prosthetic device is identified by the pre-implantationmatching method 202. In other embodiments, two or more suitableprosthetic devices are identified. In that regard, where two or moresuitable prosthetic devices are identified a specific prosthetic devicemay be selected by the during-implantation matching process 204.

Referring to FIGS. 11 and 23, after the pre-implantation matchingprocess at step 202, the method 200 continues at step 204 with aduring-implantation matching process. The during-implantation matchingprocess 204 begins at step 310 with the selection of at least twosuitable trial prosthetic devices. In some embodiments, the suitabletrial prosthetic devices are identified by the pre-implantation matchingprocess 202 described above. In some embodiments, three trial prostheticdevices are selected. Further, in one particular embodiment threedifferent sizes of a prosthetic device are selected. In otherembodiments, the selected prosthetic devices may be substantiallydifferent in shape, materials, function, and/or other properties. Insome embodiments, the trial prosthetic devices are substantially similarto the prosthetic devices that are to be permanently implanted. In someembodiments, the trial implants are the actual prosthetic devices thatare to be permanently implanted. In one embodiment, each trial has asimilar external geometry to the final implant and is formed of amaterial having similar strength properties to the final implant.However, the trial lacks the reinforcing fibers or layer. Thus, thetrial may be more easily removed from the knee joint than the finalimplant. Further, in some instances, the trial includes a visualindicator such as a marking (e.g., “TRIAL”) on the exterior or a dye inthe polymer resin to readily distinguish the trial from the finalimplant. In some instances, the trials include radiopaque markersimbedded therein to distinguish them from the final implant.

The during-implantation matching process 204 continues at step 312 withan in vivo physical testing of the prosthetic device. Generally, the invivo testing comprises introducing the trial prosthetic device into theknee joint and moving the knee joint through a series of movements. Atstep 314, the surgeon considers the fit of each prosthetic device trialand the corresponding movement of the knee joint. Based on the surgeon'sobservations at step 314, the during-implantation matching process 204concludes at step 316 with the final selection of the best prostheticdevice for the patient. Subsequently, the surgeon implants the selectedprosthetic device into the patient. In some instances, the prostheticdevice is implanted according to methods described herein.

Utilizing the during-implantation matching process 204, the surgeon candecide, based on actual physical tests, which prosthetic device bestfits a candidate knee. In that regard, in some embodiments thepre-implantation matching process is utilized to identify two or moreprosthetic devices that are suitable for use in the candidate knee. Theduring-implantation matching process is then utilized to select the bestof the suitable prosthetic devices. Accordingly, the during-implantationmatching process 204 may be utilized to confirm the results of thepre-implantation matching process 202 in some instances. In someembodiments, trial implants are utilized in the during-implantationmatching process for selecting the appropriate sized prosthetic deviceand then the actual prosthetic device of that size is subsequentlyimplanted. In some embodiments, three sizes of prosthetic devices and/ortrials are taken to surgery. Typically, the three sizes will be the bestfit prosthetic device identified in the pre-implantation matchingprocess, and prosthetic devices slightly larger and slightly smallerthan the best fit device. According to the fit within the actualcandidate knee the surgeon identifies the best prosthetic device to use.After identifying the best fit prosthetic device during surgery, thesurgeon implants the surgical device.

Surgical Protocols

Referring now to FIG. 24, shown therein is a block diagram of a surgicalprotocol 320 according to one aspect of the present disclosure.Generally, the surgical protocol 320 relates to the implantation of aprosthetic device into the knee joint of a patient. In the specificallydescribed embodiments, the surgical protocol 320 relates to theimplantation of a surgical device for replacing a medial meniscus. Inother embodiments, similar surgical protocols are utilized for replacinga lateral meniscus with a surgical device. In some instances, thesurgical procedure replaces both the medial and lateral menisci with aprosthetic device.

The surgical protocol 320 begins at step 322 where an arthroscopy isperformed. In some embodiments, a leg holder or post is utilized. Insuch embodiments, the leg holder or post may be utilized in subsequentsteps to facilitate application of a valgus force, ease insertion ofimplant, and/or otherwise assist in the performance of the surgery. Thearthroscopy is a routine arthroscopy in some embodiments. The surgicalprotocol 320 also addresses any additional inter-articular pathologiesas needed at step 322.

The surgical protocol 320 continues at step 324 with an evaluation ofthe articular cartilage of the knee joint. In some embodiments, theintegrity of the articular cartilage positioned within the medialcompartment is evaluated. Generally, the evaluation of the articularcartilage is to confirm that the patient's knee is suitable forreceiving the prosthetic device intended to be implanted. In someinstances, the articular cartilage is evaluated to identify defects inthe articular cartilage such that these defects may be treated orotherwise addressed prior to implantation of the prosthetic device.

The surgical protocol 320 continues at step 326 where the meniscus andthe fat pad are excised. In that regard, in some embodiments themeniscus is entirely removed (total meniscectomy). In other embodiments,the meniscus is partially removed (partial meniscectomy) to allow forthe introduction of the prosthetic device into the knee joint.Generally, the fat pad is excised only to the degree necessary forexposure or access to the meniscus and/or medial compartment of the kneejoint. Accordingly, in some instances the fat pad remains substantiallyintact. In other embodiments, a substantial portion of the fat pad maybe removed.

The surgical protocol 320 continues at step 328 with an enlarging of themedial portal. Generally, the medial portal is the same portal createdby the arthroscopy of step 322. However, in some embodiments the medialportal is separate from the portal created by the arthroscopy. In someembodiments, the incision is adjacent to the medial border of thepatella tendon. The medial portal is enlarged to accommodate theinsertion of the prosthetic device or implant into the knee joint. Insome embodiments, the incision or portal is enlarged to a size betweenapproximately 4.0 cm and approximately 6.0 cm. However, depending on thesize of the implant, the flexibility of the implant, and/or otherfactors, the size of the opening may be larger or smaller in otherinstances.

The surgical protocol 320 continues at step 330 with accessing themedial cavity of the knee joint. In some instances, accessing the medialcavity comprises opening the capsule and retinaculum to provide accessto the medial cavity. Further, in some instances any remaining portionsof the anterior meniscus rim are removed or excised when gaining accessto the medial cavity.

After gaining access to the medial cavity, the surgical protocol 320continues at step 332 with the insertion of one or more trial implantsinto the knee joint. The trial implants may represent different sizes ofthe same implant, different types of implants, and/or combinationsthereof. In some embodiments, the trial implants are identified in apre-implantation matching or selection method. In one particularinstance, the pre-implantation matching process 202 discussed above isutilized to identify one or more suitable implants for which trialversions of the implant may be obtained. In some instances, the trialimplants are substantially similar in size and shape to the actualimplant that will be permanently implanted in the patient. In someinstances, the only difference between the trial implant and the actualimplant is the material from which the implant is made. Specifically, inone embodiment, the trial does not include reinforcing fibers. In someinstances, the trial implant and the actual implant are identical copiesof one another. In some instances, a single implant is used as both thetrial and actual implant.

Generally, a first trial implant is inserted into the knee joint. Insome instances, the first trial implant is representative of the implantidentified as the most suitable implant in a pre-implantation selectionprocess. After insertion of the trial implant into the knee joint, thefunctionality of the knee joint is checked. In that regard, the surgeonor other medical personnel moves the knee through a variety of motionssimilar to the natural motions of the knee and monitors the knee forsigns of problems. For example, in some instances the knee is monitorfor limited or excessive the ranges of motion, abnormal sounds (e.g.,clicking or grinding), non-smooth movements, implant rotation, implanttranslation, and/or other issues indicating a potential problem withusing the associated implant. If a problem or potential problem isobserved when checking the functionality of the knee, the first trialimplant is removed an alternative trial implant is inserted and kneefunctionality is checked. In some instances, the subsequent trialimplant will be one size up or down from the previous trial implant.Further, the time period for the trialing of the implant can range froma couple of minutes up to several weeks. This process repeats until asuitable trial implant is identified. In some instances, the trialimplant process is substantially similar to the during-implantationmatching process 204 discussed above.

After a suitable trial implant has been identified, the surgicalprotocol 320 continues at step 334 with the implantation of the implantor prosthetic device selected during the trialing process. Generally,the prosthetic device is implanted using any suitable implantationmethod for the associated prosthetic device. A couple of implantationmethods will now be described. In some instances, the prosthetic devicesof the present disclosure are suitable for implantation using thefollowing methods. Referring to FIG. 25, shown therein is a blockdiagram of a method 340 of implanting a prosthetic device into apatient's knee according to one aspect of the present disclosure. Insome instances, the method 340 is utilized as the implantation step 334of the surgical protocol 320. The method 340 will be described withrespect to a “floating” implant, i.e., an implant that does notpenetrate the bone or mate with a device that penetrates bone. However,in other instances a similar method may be utilized with an implant thatis fixedly secured to bone by penetrating bone or mating with a devicethat penetrates the bone.

The method 340 begins at step 342 where the patient's knee is fullyflexed. That is, the patient's knee is put in full flexion. After thepatient's knee has been fully flexed, the method 340 continues at step344 where the prosthetic device is positioned onto the medialcompartment of the tibia. As explained above, in one embodiment thebridge of the prosthetic device is folded slightly inward into a reducedsize insertion configuration (see FIG. 9 a for example) as it is passedinto the knee joint. Once the bridge of the prosthetic device reachesthe femoral notch, the bridge resiliently moves to its anchoringconfiguration (see FIG. 9 b for example). The method 340 continues atstep 346 where the posterior rim or edge of the prosthetic device ispositioned within the gap between the femur and the tibia adjacent theposterior portion of the femur. With the prosthetic device positioned onthe medial compartment and the posterior rim in the gap between thefemur and tibia, the method 340 continues at step 348 where the knee isextended and a valgus force is applied to the knee. In some instances,the knee is extended to about a 30 degree flexion. In other instances,the knee is extended less or more. This secures the implant within theknee joint and engages the implant with both the medial compartment ofthe tibia and the femur. Subsequently, the shape of the implant and thecompression forces applied across the implant keep the implant in placewithin the knee. In some instances, the prosthetic device 100 asdescribed above is implanted using the method 340.

Referring now to FIG. 26, shown therein is a block diagram of a method350 of implanting a prosthetic device into a patient's knee according toone aspect of the present disclosure. In some instances, the method 350is utilized as the implantation step 334 of the surgical protocol 320.The method 350 will be described with respect to a “floating” implant,i.e., an implant that does not penetrate the bone or mate with a devicethat penetrates bone. However, in other instances a similar method maybe utilized with an implant that is fixedly secured to bone bypenetrating bone or mating with a device that penetrates the bone.

The method 350 begins at step 352 where a traction suture is inserted.In some instances the traction suture is inserted to theposterior-medial side of where the prosthetic device will be positionedand extends through the posterior-medial soft tissue structuresenveloping the knee. In other embodiments, the traction suture isotherwise positioned adjacent and/or within the knee joint to assist ininsertion of the prosthetic device into the medial cavity. It should benoted that in some instances the traction suture is inserted after apartial insertion of the prosthetic device into the knee joint. Themethod 350 continues at step 354 where the patient's knee is fullyflexed. That is, the patient's knee is put in full flexion. After thepatient's knee has been fully flexed, the method 350 continues at step356 where the prosthetic device is positioned onto the medial condyle ofthe tibia. The method 350 continues at step 358 where the posterior rimor edge of the prosthetic device is positioned within the gap betweenthe femur and the tibia adjacent the posterior portion of the femur.With the prosthetic device positioned on the medial condyle and theposterior rim in the gap between the femur and tibia, the method 350continues at step 360 where the knee is extended and a valgus force isapplied to the knee. The method 350 continues at step 362 where theimplant is pulled into its final position while applying tension withthe traction suture. In some instances, the traction suture helpsfacilitate positioning of the implant. In some embodiments, the tractionsuture is utilized to urge the implant into the medial cavity. In otherembodiments, the traction suture is utilized to maintain an opening tothe medial cavity to allow the implant to inserted therethrough. Withthe prosthetic device secured within the knee joint, the shape of theimplant and the compression forces applied across the implant duringloading of the knee prevent the implant from slipping out of place.

Referring again to FIG. 24, the method 320 continues at step 336 withchecking the knee motion with the prosthetic device implanted. In someembodiments, step 336 is substantially similar to step 332 where thetrial implants are evaluated. Accordingly, in some embodiments step 336comprises confirming the actual implant performs as suggested by themonitoring of the trial implant at step 332. If, for some reason, theknee functionality with the prosthetic device implanted is impaired, theprosthetic device may be adjusted, replaced with an alternativeprosthetic device, or otherwise modified to correct the problem. Afterthe knee motion has been checked and confirmed to be acceptable, themethod 320 concludes at step 338 with the suturing and bandaging of theknee.

Though not described in the above methods, it is fully contemplated thatin some instances, the femoral condyle and/or other aspects of the kneejoint may be surgically prepared to permit near-normal knee jointflexion after implantation. Further, the tibial plateau and/or otheraspects of the knee joint may be surgically prepared to fixedly engagethe implanted prosthetic device. Other modifications of the abovemethods will be apparent to those skilled in the art without departingfrom scope of the present disclosure.

A variety of materials are suitable for use in making the prostheticdevices of the present disclosure. Medical grade polyurethane basedmaterials especially suitable for use in the embodiments describedinclude, but are not limited to the following:

Bionate®, manufactured by Polymer Technology Group (“PTG”), apolycarbonate-urethane is among the most extensively tested biomaterialsever developed. Carbonate linkages adjacent to hydrocarbon groups givethis family of materials oxidative stability, making these polymersattractive in applications where oxidation is a potential mode ofdegradation, such as in pacemaker leads, ventricular assist devices,catheters, stents, and many other biomedical devices. Polycarbonateurethanes were the first biomedical polyurethanes promoted for theirbiostability. Bionate® polycarbonate-urethane is a thermoplasticelastomer formed as the reaction product of a hydroxyl terminatedpolycarbonate, an aromatic diisocyanate, and a low molecular weightglycol used as a chain extender. The results of extensive testingencompassing Histology, Carcinogenicity, Biostability, and TripartiteBiocompatibility Guidance for Medical Devices verifies the costeffective material's biocompatibility.

Another group of suitable materials are copolymers of silicone withpolyurethanes as exemplified by PurSil™, a Silicone Polyether Urethaneand CarboSil™, a Silicone Polycarbonate Urethane. Silicones have longbeen known to be biostable and biocompatible in most implants, and alsofrequently have the low hardness and low modulus useful for many deviceapplications. Conventional silicone elastomers can have very highultimate elongations, but only low to moderate tensile strengths.Consequently, the toughness of most biomedical silicone elastomers isnot particularly high. Another disadvantage of conventional siliconeelastomers in device manufacturing is the need for cross-linking todevelop useful properties. Once cross-linked, the resulting thermosetsilicone cannot be redissolved or remelted. In contrast, conventionalpolyurethane elastomers are generally thermoplastic with excellentphysical properties. Thermoplastic urethane elastomers (TPUs) combinehigh elongation and high tensile strength to form tough, albeit fairlyhigh-modulus elastomers. Aromatic polyether TPUs can have an excellentflex life, tensile strength exceeding 5000 psi, and ultimate elongationsgreater than 700 percent. These materials are often used forcontinuously flexing, chronic implants such as ventricular-assistdevices, intraaortic balloons, and artificial heart components. TPUs caneasily be processed by melting or dissolving the polymer to fabricate itinto useful shapes.

The prospect of combining the biocompatibility and biostability ofconventional silicone elastomers with the processability and toughnessof TPUs is an attractive approach to what would appear to be a nearlyideal biomaterial. For instance, in polycarbonate-based polyurethanes,silicone copolymerization has been shown to reduce hydrolyticdegradation of the carbonate linkage, whereas in polyether urethanes,the covalently bonded silicone seems to protect the polyether softsegment from oxidative degradation in vivo. Polymer Technology Groupsynthesized silicone-polyurethane copolymers by combining two previouslyreported methods: copolymerization of silicone (PSX) together withorganic (non-silicone) soft segments into the polymer backbone, and theuse of surface-modifying end groups to terminate the copolymer chains.

Other applicable materials include PurSil™ silicone-polyether-urethaneand CarboSil™ silicone-polycarbonate-urethane which are truethermoplastic copolymers containing silicone in the soft segment. Thesehigh-strength thermoplastic elastomers are prepared through a multi-stepbulk synthesis where polydimethylsiloxane (PSX) is incorporated into thepolymer soft segment with polytetramethyleneoxide (PTMO) (PurSil) or analiphatic, hydroxyl-terminated polycarbonate (CarboSil). The hardsegment consists of an aromatic diisocyanate, MDI, with low molecularweight glycol chain extender. The copolymer chains are then terminatedwith silicone (or other) Surface-Modifying End Groups. Aliphatic (AL)versions of these materials, with a hard segment synthesized from analiphatic diisocyanate, are also available.

Many of these silicone urethanes demonstrate desirable combinations ofphysical properties. For example, aromatic silicone polyetherurethaneshave a higher modulus at a given shore hardness than conventionalpolyether urethanes—the higher the silicone content, the higher themodulus (see PurSil Properties). Conversely, the aliphatic siliconepolyetherurethanes have a very low modulus and a high ultimateelongation typical of silicone homopolymers or even natural rubber (seePurSil AL Properties). These properties make these materials veryattractive as high-performance substitutes for conventional cross-linkedsilicone rubber. In both the PTMO and PC families, some polymers havetensile strengths three to five times higher than conventional siliconebiomaterials.

Further examples of suitable materials include Surface Modifying EndGroups (SMEs) which are surface-active oligomers covalently bonded tothe base polymer during synthesis. SMEs—which include silicone (S),sulfonate (SO), fluorocarbon (F), polyethylene oxide (P), andhydrocarbon (H) groups—control surface chemistry without compromisingthe bulk properties of the polymer. The result is that key surfaceproperties, such as thromboresistance, biostability, and abrasionresistance, are permanently enhanced without additional post-fabricationtreatments or topical coatings. This technology is applied to a widerange of PTG's polymers.

SMEs provide a series of base polymers that can achieve a desiredsurface chemistry without the use of additives. Polyurethanes preparedaccording to PTG's development process couple endgroups to the backbonepolymer during synthesis via a terminal isocyanate group, not a hardsegment. The added mobility of endgroups relative to the backbonefacilitates the formation of uniform overlayers by the surface-activeend blocks. The use of the surface active endgroups leaves the originalpolymer backbone intact so the polymer retains strength andprocessability. The fact that essentially all polymer chains carry thesurface-modifying moiety eliminates many of the potential problemsassociated with additives.

The SME approach also allows the incorporation of mixed endgroups into asingle polymer. For example, the combination of hydrophobic andhydrophilic endgroups gives the polymers amphipathic characteristics inwhich the hydrophobic versus hydrophilic balance may be easilycontrolled.

Other suitable materials, manufactured by CARDIOTECH CTE, includeChronoFlex® and Hydrothane™.

The ChronoFlex®, polycarbonate aromatic polyurethanes, family ofmedical-grade segmented biodurable polyurethane elastomers have beenspecifically developed by CardioTech International to overcome the invivo formation of stress-induced microfissures.

HydroThane™, hydrophilic thermoplastic polyurethanes, is a family ofsuper-absorbent, thermoplastic, polyurethane hydrogels ranging in watercontent from 5 to 25% by weight. HydroThane™ is offered as a clear resinin durometer hardness of 80A and 93 Shore A. The outstandingcharacteristic of this family of materials is the ability to rapidlyabsorb water, high tensile strength, and high elongation. The result isa polymer having some lubricious characteristics, as well as beinginherently bacterial resistant due to their exceptionally high watercontent at the surface. HydroThane™ hydrophilic polyurethane resins arethermoplastic hydrogels, and can be extruded or molded by conventionalmeans. Traditional hydrogels on the other hand are thermosets anddifficult to process.

Additional suitable materials manufactured by THERMEDICS includeTecothante® (aromatic polyether-based polyurethane), Carbothane®(aliphatic polycarbonate-based polyurethane), Tecophilic® (high moistureabsorption aliphatic polyether-based polyurethane) and Tecoplast®(aromatic polyether-based polyurethane). Tecothane® is a family ofaromatic, polyether-based TPU's available over a wide range ofdurometers, colors, and radiopacifiers. One can expect Tecothane resinsto exhibit improved solvent resistance and biostability when comparedwith Tecoflex resins of equal durometers. Carbothane® is a family ofaliphatic, polycarbonate-based TPU's available over a wide range ofdurometers, colors and radiopacifiers. This type of TPU has beenreported to exhibit excellent oxidative stability, a property which mayequate to excellent long-term biostability. This family, like Tecoflex,is easy to process and does not yellow upon aging. Tecophilic® is afamily of aliphatic, polyether-based TPU's which have been speciallyformulated to absorb equilibrium water contents of up to 150% of theweight of dry resin.

Polyurethanes are designated aromatic or aliphatic on the basis of thechemical nature of the diisocyanate component in the formulation.Tecoflex, Tecophilic and Carbothane resins are manufactured using thealiphatic compound, hydrogenated methylene diisocyanate (HMDI).Tecothane and Tecoplast resins use the aromatic compound methylenediisocyanate (MDI). Tecoflex® is a family of aliphatic, polyether-basedTPU'S. These resins are easy to process and do not yellow upon aging.Solution grade versions are candidates to replace latex. Someformulations are formulated using polytetramethylene ether glycol(PTMEG) and 1, 4 butanediol chain extender. Carbothane is specificallyformulated with a polycarbonate diol (PCDO). These materials representthe major chemical composition differences among the various families.Aromatic and aliphatic polyurethanes share similar properties that makethem outstanding materials for use in medical devices. In general, thereis not much difference between medical grade aliphatic and aromaticpolyurethanes with regard to the following chemical, mechanical andbiological properties: high tensile strength (4,000 to 10,000 psi); highultimate elongation (250 to 700%); wide range durometer (72 Shore A to84 Shore D); good biocompatibility; high abrasion resistance; goodhydrolytic stability; can be sterilized with ethylene oxide and gammairradiation; retention of elastomeric properties at low temperature;good melt processing characteristics for extrusion, injection molding,etc.

With such an array of desirable features, it is no wonder that bothaliphatic and aromatic polyurethanes have become increasingly thematerial of choice in the design of medical grade components. There are,however, distinct differences between these two families of polyurethanethat could dictate the selection of one over the other for a particularapplication:

In their natural states, both aromatic and aliphatic polyurethanes areclear to very light yellow in color. Aromatics, however, can turn darkyellow to amber as a result of melt processing or sterilization, or evenwith age. Although the primary objection to the discoloration ofaromatic clear tubing or injection molded parts is aesthetic, theyellowing that is caused by the formation of a chromophore in the NMIportion of the polymer does not appear to affect other physicalproperties of the material. Radiopaque grades of Tecothane also exhibitsome discoloration during melt processing or sterilization. However,both standard and custom compounded radiopaque grades of Tecothane havebeen specifically formulated to minimize this discoloration.

Aromatic polyurethanes exhibit better resistance to organic solvents andoils than do aliphatics—especially as compared with low durometer (80 to85 Shore A) aliphatic, where prolonged contact can lead to swelling ofthe polymer and short-term contact can lead to surface tackiness. Whilethese effects become less noticeable at higher durometers, aromaticsexhibit little or no sensitivity upon exposure to the common organicsolvents used in the health care industry.

Both aliphatic and aromatic poly-ether based polyurethanes softenconsiderably within minutes of insertion in the body. Many devicemanufacturers promote this feature of the urethane products because ofpatient comfort advantage as well as the reduced risk of vasculartrauma. However, this softening effect is less pronounced with aromaticresins than with aliphatic resins.

Tecothane, Tecoplast and Carbothane melt at temperatures considerablyhigher than Tecoflex and Tecophilic. Therefore, processing by eitherextrusion of injection molding puts more heat history into productsmanufactured from Tecothane, Tecoplast and Carbothane. For example,Tecoflex EG-80A and EG-60D resins mold at nozzle temperatures ofapproximately 310 degrees F. and 340 degrees F. respectively whileTecothane and Carbothane products of equivalent durometers mold atnozzle temperatures in the range of 380 degrees F. and 435 degrees F.

Additional materials of interest include Tecogel, a new member to theTecophilic family, a hydrogel that can be formulated to absorbequilibrium water contents between 500% to 2000% of the weight of dryresin, and Tecoplast®, a family of aromatic, polyether-based TPU'sformulated to produce rugged injection molded components exhibiting highdurometers and heat deflection temperatures.

Additional potentially suitable materials include four families ofpolyurethanes, named Elast-Eon™, which are available from AorTechBiomaterials.

Elast-Eon™ 1, a Polyhexamethylene oxide (PFMO), aromatic polyurethane,is an improvement on conventional polyurethane in that it has a reducednumber of the susceptible chemical groups. Elast-Eon.™.2, a Siloxanebased macrodiol, aromatic polyurethane, incorporates siloxane unto thesoft segment. Elast-Eon.™.3, a Siloxane based macrodiol, modified hardsegment, aromatic polyurethane, is a variation of Elast-Eon.™.2 withfurther enhanced flexibility due to incorporation of siloxane into thehard segment. Elast-Eon™ 4 is a modified aromatic hard segmentpolyurethane.

Bayer Corporation also produces candidate materials. Texin 4210 andTexin 4215 are thermoplastic polyurethane/polycarbonate blends forinjection molding and extrusion. Texin 5250, 5286 and 5290 are aromaticpolyether-based medical grade materials with Shore D hardness ofapproximately 50, 86, and 90 respectively for injection molding andextrusion.

Manufacturing Procedures

The prosthetic devices of the present disclosure may be manufactured invarious sizes, so that typical applications can be satisfied by a“stock” unit. Accordingly, a surgeon could, during an implantationprocedure, select a correctly sized device from the selection of stockunits. Alternatively, in another embodiment, a replacement meniscus iscustom manufactured for a particular patient utilizing characteristicsdetermined by medical imaging techniques, such as MRI, coupled withcomputer aided manufacturing (CAM) techniques.

In some embodiments, the prosthetic device is a melt mold compositeimplant composed of two biocompatible materials: PTG Bionate®Polycarbonate-Urethane (PCU), 80 Shore A, matrix material and ultra highmolecular weight polyethylene (UHMWPE) reinforcement material. In someparticular embodiments, a prosthetic device formed of PCU and reinforcedcircumferentially with DSM Dyneema® fibers results in a desirabledistribution of loads on the underlying articulation surfaces of theprosthetic device. Accordingly, referring generally to FIGS. 27-35aspects and methods of manufacturing such a device will be described.

Referring more specifically to FIGS. 27, 28, 29, and 31, shown thereinis a prosthetic device 370 according to one aspect of the presentdisclosure. Generally, the prosthetic device 370 includes a core 372surrounded by an outer portion 374. The prosthetic device 370 includesan upper articulation surface 376 and an opposing lower articulationsurface 378 (FIG. 29). The upper articulation surface 376 is configuredto engage the femur while the lower articulation surface 378 isconfigured to engage the tibia. In some embodiments, the prostheticdevice 370 is formed via an injection molding process that substantiallylimits the defects, imperfections, and/or process residue in and on thearticulation surfaces. In that regard, the articulation surfaces mayobtain a smoothness substantially similar to that of the surfaces of themold in which they are formed. In some instances, the mold surfaces aremirror polished to an optical polish between about 0.05 Ra and 0.4 Ra.

The prosthetic device 370 is imbedded with fibers (not shown). In someinstances, the fibers are positioned circumferentially around theprosthetic device 370 between the core 372 and the outer portion 374. Inthat regard, the core 372 includes features to facilitate positioning ofthe fibers within the prosthetic device 370 in some embodiments. Forexample, referring more specifically to FIG. 28, shown therein is adiagrammatic perspective view of the core 372 according to one aspect ofthe present disclosure. As shown, the core 372 includes an upper rim 380and a lower rim 382 defining an outer boundary of the core. Between theupper and lower rims 380, 382 the core 372 includes a series ofalternating projections and recesses. In the current embodiment, thecore includes projections 384, 386, 388, and 390 between the upper rim380 and the lower rim 382. Referring to FIG. 29, between the rims 380,382 and the projections the core 372 includes recesses 392, 394, 396,398, and 400. In some embodiments, the recesses 392, 394, 396, 398, and400 are sized and shaped to receive the fibers to be imbedded within thedevice 370. In some instances, the projections 384, 386, 388, 390 andthe recesses 392, 394, 396, 398, 400 are configured such that the fibersmay be wound around the core 372.

In the present embodiment, the recesses 392, 394, 396, 398, and 400increase in size along the height of the core 372 from the upper rim 380to the lower rim 382. Accordingly, the recess 392 adjacent the upper rim380 and projection 384 is the smallest of the recesses, while the recess400 adjacent the lower rim 382 and projection 390 is the largest of therecesses. Thus, in the current embodiment the lower portion of theprosthetic device 370 as viewed in FIG. 29 is configured to receive agreater number of fibers than the upper portion of the device. Further,as shown, each of the recesses 392, 394, 396, 398, and 400 are taperedsuch that the recess is wider adjacent the outer portion of the recessthan the inner portion of the recess. In some instances, this is aresult of injection molding the core 372 with a mold/insert having acorresponding tapered or angled shape. The tapering or angling themold/inserts in this manner to create the tapered or angled recessesallows the mold/inserts to be separated from the core 372 after theinjection molding process easier and without causing damage to the core.

Generally, the shape and size and of the projections and recesses of thecore 372 are tailored or selected to achieve the desired fiberdistribution through the device. Accordingly, in some instances all ofthe projections and recesses are substantially the same size. In otherinstances, the projections, recesses, or other aspects of the prostheticdevice associated with the distribution of the imbedded fibers varyalong the height, circumference, length, width, or other aspect of theprosthetic device to accommodate a desired fiber distribution. In thatregard, in some instances, the projections and recesses aresubstantially annular extending completely around the core 372. In otherinstances, such as the embodiment illustrated in FIG. 28, theprojections and recesses comprise one or more discrete sections aroundthe core 372.

In some instances, the upper and lower rims 380, 382 of the core 372 areconfigured to mate with the outer portion 374 of the prosthetic device370 such that the outer portion is substantially positioned between theupper and lower rims. In that regard, the upper and lower rims 380, 382may comprise part of the upper and lower articulation surfaces 376, 378,respectively, such that the outer portion 374 may be injection molded orotherwise attached to the core 372 without adversely affecting thearticulation surfaces of the prosthetic device 370. In some instances,however, the core 372 does not include the upper and lower rims 380,382. For example, referring to FIG. 30 shown therein is a core 402according to an alternative embodiment of the present disclosure thatdoes not include upper and lower rims. The core 402 is otherwisesubstantially similar to the core 372 in other respects. In someinstances, the outer portion 374 of the prosthetic device 370 comprisesan outer area or boundary of the upper and lower articulating surfacesof the prosthetic device. For example, in some instances the outerportion 374 is molded around the core 402 such that the outer portiondefines at least a portion of the upper and lower articulating surfacesof the prosthetic device. In one such embodiment, at least the upper andlower surfaces of the outer portion 374 have a smoothness substantiallysimilar to the upper and lower articulating surfaces 376, 378 of thecore.

As noted, in other instances, the outer portion 374 is positionedsubstantially between the upper and lower rims 380, 382 of the core 372.Referring more specifically to FIG. 31, the outer portion 374 comprisesan inner surface 404, and outer surface 406, an upper surface 408, and alower surface 410. While the inner surface 404 is shown as beingsubstantially smooth, it is understood that in some embodiments theouter portion 374 is injection molded around the core 372 and/or thefibers surrounding the core. In such embodiments, the inner surface 404will substantially match the contours of the core and fibers adjacentthereto. In other embodiments, however, the outer portion 374 comprisesa substantially smooth inner surface 404 as shown. Where the outerportion 374 is positioned substantially between the upper and lower rims380, 382 the upper and lower surfaces 408, 410 interface with the rims.In that regard, in some instances, the engagement surfaces of the upperand lower rims 380, 382 include features to facilitate engagementbetween the outer portion 374 and the core 372. For example, theengagement surfaces of the upper and lower rims 380, 382 may beroughened, textured, knurled, include projections and/or recesses, orotherwise be shaped or treated to enhance engagement between the outerportion 374 and the core 372.

In some embodiments, the fibers of the prosthetic device 370 are fullyimbedded inside the hosting material of the core 372 and/or the outerportion 374 to prevent contact between the fibers and articulationsurfaces of the device. In this manner the fibers are prevented fromcontacting the host tissue of the patient as well. In some embodiments,the fibers are formed of UHMWPE while the core 372 and/or outer portion374 are formed of a PCU. In such embodiments, the injection moldingprocess is performed in a manner that does not affect the form,mechanical properties, or stability of the UHMWPE fibers. In thatregard, generally the UHMWPE has a lower melting temperature than thePCU such that standard injection molding processes that would inject PCUaround the UMWPE fibers will adversely affect the properties of theUHMWPE fibers. Accordingly, in some instances the prosthetic device 370is manufactured utilizing methods of the present disclosure thatpreserve the desired material properties of the UHMWPE fibers even whenutilized with PCU.

In some embodiments, the fibers are configured to distribute the loadacross the prosthetic device 370 in a manner that mimics a naturalmeniscus. In that regard, the amount of fibers, the type of fibers,distribution of the fibers, and/or the location of the fibers is alteredin some embodiments to achieve a desired load distribution. Further,these attributes of the fiber may vary within a single implant dependingon the position within the implant. For example, in some instances thenumber or density of fibers varies along the height of the prostheticdevice. In some instances, the fiber characteristics are determined atleast partially based on the patient receiving the prosthetic device370. For example, factors such as the size of the patient's kneeanatomy, the patient's weight, the patient's anticipated activity level,and or other aspects of the patient are taken into consideration whendetermining the characteristics of the fibers imbedded in the prostheticdevice 370. In some instances, a fiber incorporation ratio (FIR) istaken into consideration. Generally, the fiber incorporation ratio isrepresentative of the amount or percentage of fibers within theprosthetic device 370 as compared to the matrix material or basematerial. In some embodiments, the fiber incorporation ratio is measuredas the area of the fibers divided by the area of the prosthetic deviceas view in a cross-section of the device, or

${FIR} = {\frac{{Area}_{FiberCS}}{{Area}_{DeviceCS}}.}$

Referring to FIG. 32, shown there is a chart setting forth fiberincorporation ratios for prosthetic devices based on patient weight andactivity levels according to one aspect of the present disclosure. Asillustrated, in this embodiment the fiber incorporation ratio isdetermined based on the patient's weight and activity level, which aregrouped into ranges. Specifically, the patient's weight is grouped intothree categories: less than 60 Kg, between 60 Kg and 110 Kg, and greaterthan 110 Kg. In other embodiments, the patient's weight is grouped intoa greater number of categories or the patient's specific weight isutilized. The patient's activity level is also grouped into threecategories: low activity, moderate activity, and high activity. Again,in other embodiments the patient's activity level is grouped into agreater number of categories and/or characterized based on types ofactivities. In other instances, other factors are taken intoconsideration in determining the fiber incorporation. As shown in FIG.32, generally the greater the patient's weight and activity the level,the greater the fiber incorporation ratio. Generally, in accordance withFIG. 32 the fiber incorporation ratio ranges from about 0.1% to about1.2%. In other embodiments, however, the fiber incorporation ratioranges from about 0.0% (i.e., no fibers) to about 50%.

Referring to FIGS. 33 and 34, shown therein are prosthetic devices 430and 440 having different fiber incorporation ratios according to thepresent disclosure. The prosthetic device 430 of FIG. 33 includes anupper articulation surface 432, a lower articulation surface 434, and anouter portion 436 reinforced with fibers 438. The prosthetic device 430comprises a relatively low fiber incorporation ratio. The fibers 438 aredistributed equally along the height of the prosthetic device 430 andadjacent the outer boundary of the device. The prosthetic device 440 ofFIG. 34 also includes an upper articulation surface 442, a lowerarticulation surface 444, and an outer portion 446 reinforced withfibers 447. However, the fibers 447 of the prosthetic device 440 are notdistributed equally along the height of the device. As shown, in theprosthetic device 440 the fibers 447 are generally aligned in rows 448,450, 452, and 454 of increasing fiber density from the upper portion ofthe device towards the lower portion of the device. In some aspects, theprosthetic device 440 is representative of a device that utilizes thecore 372 discussed above having varying sized recesses for receiving thefibers. In that regard, the rows 448, 450, 452, and 454 of varying fiberdensity correspond to the recesses of the core having varying sizes forreceiving the fibers.

Referring now to FIG. 35, shown therein is a block diagram of a method460 for manufacturing a prosthetic device according to one aspect of thepresent disclosure. Generally, the method 460 comprises three steps: acore injection step 462, a fiber winding step 464, and an outer portioninjection step 466. The method 460 begins at step 462 with the injectionmolding of the core of the prosthetic device. In some instances, thecore is molded to be substantially similar to the cores 372 or 402described above. Accordingly, in such embodiments the mold into whichthe material is injected is shaped as the negative of the core 372 orcore 402. In some instances, to avoid over-lapping of the PCU in theouter portion injection process and to ensure that the contact surfacesof the implant remain smooth and free of defects, the upper and lowerrims of the core are molded to allow the outer portion of the prostheticdevice to be subsequently injected between the rims without affectingthe articulation surfaces of the device.

After molding of the core at step 462, the method 460 continues at step464 with the winding of fiber around the core. In some embodiments, thecore is allowed to completely set up prior to winding the fibers aroundthe core. In other instances, the core is not completely set up prior tothe winding such that at least a first layer of the fibers is at leastpartially imbedded within the core. In some embodiments, the windingprocess 464 is performed by a winding machine that controls the amountof fibers in each tunnel or recess of the core and maintains the tensionof the fibers during the winding process. As discussed above, thetunnels of core are sized to allow incorporation of different amounts offibers in some embodiments. Accordingly, in some instances between 1 and20 fibers are placed in each tunnel depending on the location of thetunnel along the implant height.

During the winding process 464 the fibers will be tensioned with a forcebetween about 5 N and about 78 N. In some instances, the tension on thefibers is selected so that the resultant prosthetic device ispretensioned such that the prosthetic device stretches upon implantationand loading. In some instances, the pretensioning results in theprosthetic device having a reduced size relative to the natural meniscusin the pretensioned state. In some embodiments, the tension on the fiberis determined based on the chart of FIG. 36 setting forth tensioningforces for various fibers based on the property of the fibers accordingto one aspect of the present disclosure. In some instances, the fiber iswound at approximately 10% of the fiber's maximum tension. For example,if the fibers maximum tension force is approximately 50 N, then in someinstances the fiber is wound around the core of the prosthetic devicewith a force of approximately 5 N.

After the fibers have been wound around the core, the method 460continues at step 466 with the injection molding of the outer portion ofthe prosthetic device. In some instances, prior to the outer portioninjection 466, the core mold will be warmed to approximately 100° C. toimprove the adhesion between the core and the outer surface portion.However, based on manufacturer instruction, long exposure totemperatures higher than 150° C. will cause melting of UHMWPE fibers. Ashort exposure to temperature higher than 150° C. (thermal shockcondition), however, will not affect the structural or mechanicalproperties of the UHMWPE fibers. Accordingly, in some instances theouter portion is injected at a temperature above the melting point ofthe UHMWPE fibers. In one specific embodiment, a polycarbonatepolyethylene is injected at a temperature of approximately 160° C.Accordingly, in embodiments where UHMWPE fibers are utilized, one ormore of the following steps are utilized to minimize the time the fibersare exposed to the elevated temperature to prevent melting of the fibersand/or adverse material changes to the fibers. In some instances,immediately after the outer surface injection, the mold is cooled toambient room temperature (approximately 25° C.) by circulating coldfluid through cooling tunnels within the mold used in forming theprosthetic device. Further, in some instances, the amount of thematerial injected into the mold for the outer portion is kept to aminimum. The smaller mass of injected material cools faster reducing theexposure time to the increased temperatures.

In some embodiments, the two-phase molding process (steps 462 and 466)utilizes a single modular mold structure composed of several parts. Forexample, in some instances the mold comprises an outer structure shapedto correspond to the overall shape of the prosthetic device and includesat least one removable insert shaped for molding the core of theprosthetic device. In that regard, the mold is modified by removing theinserts between the two injection phases 462 and 466. The removal of theinserts allows the winding of fibers around the core in some instances.Generally, removal of the inserts after the core injection 462 does notrequire the removal or destruction of the previously injected materialforming the core. Rather, as discussed above the tunnels or recessesalong the perimeter of the core are shaped to allow smooth release ofthe inserts of the mold that shape these tunnels. For example, in someembodiments, the mold inserts are tapered to facilitate removal. In someinstances, the mold inserts are polished or otherwise have smoothsurfaces to limit the friction between the injected core and theinserts. In some embodiments, the mold is made of aluminum, steel, othermetals, and/or combinations thereof. In situations where aluminum and/oraluminum steel are utilized, the surfaces that come into contact withthe injected material are coated with hard anodize. In some instances, alayer of approximately 10 μm of hard anodize is utilized. In otherinstances, a thicker or thinner layer of hard anodize is utilized.

In some embodiments, the prosthetic devices are formed of a cartilagereplacement material having structural and material propertiessimulating the functionality of a natural meniscus. Generally, thematerial provides a pliable articulating surface equivalent to thevarious load bearing forms of cartilaginous tissues of the body, such ashyaline (articular) cartilage and fibro-cartilage (e.g. intervertebraldiscs, knee meniscus, etc.). The material provides shock absorption andreduction in the impact intensity exerted on the adjacent bones and/orthe implant itself. In some instances, the shock absorption functionreduces patient pain, reduces wear on the device, and/or providesgreater mobility to the patient. The material is resiliently deformable.Specifically, the material deforms under the natural stresses applied bythe patient's body such that material stresses of the prosthetic deviceare handled in a manner similar to that of the natural cartilage toachieve pressure distributions within the material and on thearticulating surfaces similar to natural, healthy cartilage.

In one embodiment, the material is a composite material composed of apliable biocompatible matrix material imbedded with fibers or otherreinforcement material. The specific composite structure of the materialis based, in some instances, on the structural characteristics ofnatural cartilage, which consists of a cartilage matrix imbedded with ahighly orientated collagen fiber network or collagen fibrils. Similar tonatural cartilage, the material is able to withstand high impact forcesyet maintain its form due to its reinforced resilient compositestructure. In that regard, a synergism between the matrix material andthe fiber material results in material properties unavailable from theeach of the materials individually. Specifically, the pliable matrixmaterial provides a damping or cushioning effect and distributespressure by permitting local material flow or deformation. Thereinforcement material, on the other hand, maintains and stabilizes theoverall design shape of the prosthetic device by restraining or limitingthe flow of the matrix material. In that regard, the reinforcementmaterial or fiber material bears a high portion of the stresses that acton the prosthetic device. In some instances, compressive loads exertedon the prosthetic device are transformed into tensile loading on thereinforcement or fiber materials due to the shape of the prostheticdevice and the orientation of the fibers therein. In that regard, theprosthetic device 100 discussed above functions in this manner in someinstances. That is, compression loading of the prosthetic device 100 isconverted into tensile loading on the imbedded fiber 124 due to thedeformation or stretching of the prosthetic device. These materials havebeen shown to produce load distributions under compression similar tonatural cartilaginous tissue.

In some embodiments, the resilient matrix material comprises abiocompatible polymer. In some instances, the polymer is a polycarbonatepolyurethane. In one specific embodiment, the matrix material is PTGBionate® Polycarbonate-Urethane (PCU), 80 Shore A. The high modulusreinforcement material utilized in the application may be any one of thefollowing: Ultra High Molecular Weight Polyethylene (UHMWPE) fiber, forexample DSM Dyneema® Purity; Para-aramid synthetic fiber, for exampleDuPont™ Kevlar, Kevlar29, Kevlar49; carbon; stainless-steel; titanium;nickel-titanium (Nitinol); and/or other suitable reinforcementmaterials. In that regard, the fibers may be employed in a monofilamentor multifilament form as a single strand or a multiple fiber twine, in adiameter range of 0 to 1 mm.

A few specific embodiments of the cartilage replacement material willnow be described. These embodiments are understood to be exemplary anddo not limit the various ways in which reinforcement material may beimbedded or otherwise distributed within a matrix material to simulatethe properties of natural cartilage in accordance with the presentdisclosure. Generally, the reinforcement material can be imbedded in thematrix material in either a fiber form (straight, wound, or otherwise),in a complex mesh form, and/or any combination of thereof depending onthe desired functionality and geometry of the application. In someinstances, the fiber distribution varies through different portions ofthe matrix material. In that regard, in some embodiments the fiberdistribution is varied such that the mechanical properties of thematerial divert high stresses from prone areas.

Overall, the fiber incorporation ratio of the material may vary betweenabout 0 percent and about 50 percent, when measured as the fiber crosssection area relative to the total material cross section area. In someinstances, the fiber incorporation ratio is varied through the materialto obtain a desired functionality and/or material properties. Forexample, the amount of fibers incorporated into the material may varyaccording to position (i.e. the amount of fibers incorporated indifferent material depths and locations is varied) based on the intendedapplication of material. Generally, higher contact stress areas areassociated with employing of higher a number of fibers. Accordingly, insome instances fibers are concentrated in the high contact stress areasof the material or prosthetic device. The specific number of fibersutilized depends on such factors as patient activity level, patient bodyweight, the matrix material, the fiber material, implant shape, desiredfunctionality, and/or other factors. In some instances, the distributionof fibers and/or the fiber incorporation ratio are determined by acomputational finite-element analysis.

Referring more specifically to FIG. 37, shown therein is a diagrammaticperspective view of a representative material 460 having a linear fiberconfiguration according to one aspect of the present disclosure. In thatregard, the material 460 includes a matrix material 462 imbedded with aplurality of fibers 464. As shown, the fibers 464 extend substantiallyparallel to one another along a length of the material. In someinstances, the fibers 464 are aligned such that all of the fibers arepositioned substantially within the same plane within the matrixmaterial. In other embodiments, the fibers are aligned in multipleplanes within the matrix material. In yet other embodiments, the fibersare distributed throughout the matrix material but all extend linearlyin substantially the same direction. Generally, the fibers 464 may bedistributed through the matrix material 462 in any manner, orientation,or combination such that the fibers 464 extend linearly andsubstantially parallel to one another.

Referring more specifically to FIGS. 38 and 39, shown therein is arepresentative material 470 having a fiber mesh configuration accordingto one aspect of the present disclosure. Specifically, FIG. 38 is adiagrammatic perspective view of the material 470 and FIG. 39 is apartial cross-sectional view of the material 470 taken along sectionline 39-39 of FIG. 38. The material 470 includes a matrix material 472imbedded with a plurality of fibers or fiber mesh 474. As shown in FIG.39, in the present embodiment the fibers 474 include an upper fiber meshportion 476 and a lower fiber mesh portion 478. As shown, each of thefiber mesh portions 476, 478 comprise interlocking, interweaved, and/oroverlying fibers 474 organized in a grid pattern. In the presentembodiments, the fibers interface at substantially perpendicular anglesto define the grid pattern. That is, a first grouping of fibers extendsubstantially parallel to one another along a first axis of the materialand a second grouping of fibers extend substantially parallel to asecond axis of the material substantially perpendicular to the firstaxis to define grid pattern of the fiber mesh. In other embodiments, thefiber mesh may comprise alternative grid patterns, angles, and/ororientations. In the present embodiment, the upper and lower fiber meshportions 476, 478 are substantially planar and extend substantiallyparallel to one another through the material 470. In some instances, thefiber mesh portions 476, 478 extend at non-parallel angles with respectto one another. In some embodiments, the material 470 includes a greateror fewer number of fiber mesh portions. In some instances, the fibermesh portions are not substantially planar. Generally, the fiber meshportions may be distributed through the matrix material 472 in anymanner, orientation, or combination as desired.

Referring more specifically to FIGS. 40 and 41, shown therein is arepresentative material 480 having winded fiber configuration accordingto one aspect of the present disclosure. Specifically, FIG. 40 is adiagrammatic perspective view of the material 480 and FIG. 41 is apartial perspective cross-sectional view of the material 480 taken alongsection line 41-41 of FIG. 40. The material 480 includes a matrixmaterial 482 imbedded with a plurality of fibers 484. In the presentembodiment, the fibers 484 are disposed annularly within the matrixmaterial 482. In some instances, each of the fibers 484 is wound aroundor into the material 482 to form the annular structure. In the presentembodiment, the fibers 484 are substantially aligned within a verticalplane of the material such that the fibers generally define acylindrical shape. In other embodiments, the fibers 484 may comprisealternative orientations and/or patterns. In that regard, the fibers arewound into oblong, rectangular, other geometrical, and/or othernon-geometrical shapes in some instances. Further, in some instances,multiple groupings of fibers are disposed within the material. In onespecific embodiment, multiple annular rings of fibers are disposedconcentrically within the matrix material. Generally, the fibers may bewound into or around the matrix material 472 in any manner, orientation,or combination as desired.

In the illustrated embodiments of FIGS. 37-41, the matrix materials areillustrated as being at least partially translucent, while the fibersare illustrated as being substantially opaque such that the fibers arevisible through the matrix material. In other instances, however, thematrix material is substantially opaque and/or the fibers aretranslucent and/or substantially the same color as the matrix materialsuch that the fibers are not visible through the matrix material.

The composite materials described above may be utilized for formingprosthetic devices. For example, in some instances the compositematerials are utilized for knee joints (including meniscus and totalknee joints), hip joints (including acetabular cups), shoulder joints,elbow joints, finger joints, and other load bearing and/or non-loadbearing prosthetic devices.

It should be appreciated that in some instances the prosthetic devicesof the present disclosure are formed by other processes than thosedescribed herein. These manufacturing processes include any suitablemanufacturing method. For example, without limitation any of thefollowing manufacturing methods may be utilized: injection moldingincluding inserting inserts; compression molding including insertinginserts; injection-compression molding including inserting inserts;compression molding of prefabricated elements pre-formed by any of theabove methods including inserting inserts; spraying including insertinginserts; dipping including inserting inserts; machining from stocks orrods; machining from prefabricated elements including inserting inserts;and/or any of the above methods without inserts. Further, it should beappreciated that in some embodiments the prosthetic devices of thepresent disclosure are formed of medical grade materials other thanthose specifically identified above. In that regard, in some embodimentsthe prosthetic devices are formed of any suitable medical gradematerial.

While the principles of the present disclosure have been set forth usingthe specific embodiments discussed above, no limitations should beimplied thereby. Any and all alterations or modifications to thedescribed devices, instruments, and/or methods, as well as any furtherapplication of the principles of the present disclosure that would beapparent to one skilled in the art are encompassed by the presentdisclosure even if not explicitly discussed herein. It is alsorecognized that various presently unforeseen or unanticipatedalternatives, modifications, and variations of the present disclosuremay be subsequently made by those skilled in the art. All suchvariations, modifications, and improvements that would be apparent toone skilled in the art to which the present disclosure relates areencompassed by the following claims.

1. A prosthetic device for replacing a damaged meniscus, the prostheticdevice comprising: a central portion having a concave upper surface forengagement with a portion of a femur and an opposing partially concavelower surface for engagement with a portion of a tibia, the centralportion comprising a flexible resilient polymeric material having amodulus of elasticity between about 1 MPa and about 10 MPa, wherein thecentral portion has a minimum thickness less than about 3 mm between theupper surface and the lower surface; an outer portion surrounding thecentral portion and having an increased thickness relative to thecentral portion, the outer portion comprising the resilient polymericmaterial and tensioned with at least one reinforcing fiber embeddedwithin the resilient polymeric material; wherein the outer portion issized and shaped such that a compression force imparted on theprosthetic device by the femur and the tibia displaces the outer portionradially outward from the central portion; wherein the outer portion isfurther sized and shaped such that the prosthetic device is configuredfor implantation within a knee joint between the femur and the tibiawithout being rigidly fixed to either of the femur and the tibia and theouter portion prevents unwanted expulsion of the prosthetic device fromthe knee joint when the prosthetic device is implanted within the kneejoint without being rigidly fixed to either of the femur and the tibia.2. The prosthetic device of claim 1, wherein the at least onereinforcing fiber is tensioned at a force between about 5 N and about 78N.
 3. The prosthetic device of claim 2, wherein the at least onereinforcing fiber is tensioned at a force between about 7 N and about 8N.
 4. The prosthetic device of claim 2, wherein the at least onereinforcing fiber is tensioned at a force between about 8 percent andabout 12 percent of the at least one reinforcing fiber's maximumtension.
 5. The prosthetic device of claim 1, wherein the compressionforce imparted on the prosthetic device is at least partiallytransformed into a tensile load on the at least one reinforcing fiber.6. The prosthetic device of claim 5, wherein the at least onereinforcing fiber extends completely around the central portion withinthe outer portion.
 7. The prosthetic device of claim 1, wherein thecentral portion stretches as the outer portion is displaced radiallyoutward by the compression force.
 8. The prosthetic device of claim 7,wherein a contact area between the portion of the femur and the uppersurface of the central portion increases with the stretching of thecentral portion.
 9. The prosthetic device of claim 7, wherein a contactarea between the portion of the tibia and the lower surface of thecentral portion increases with the stretching of the central portion.10. The prosthetic device of claim 1, wherein the resilient polymericmaterial is a medical grade polyurethane based material.
 11. Theprosthetic device of claim 10,wherein the resilient polymeric materialis a polycarbonate polyurethane.
 12. The prosthetic device of claim 11,wherein the at least one embedded fiber comprises an ultra highmolecular weight polyethylene.
 13. The prosthetic device of claim 1,wherein the outer portion comprises a first section comprising asemi-ellipsoidal profile similar to a natural meniscus.
 14. Theprosthetic device of claim 13, wherein the outer portion comprises abridge portion connecting first and second ends of the semi-ellipsoidalprofile of outer portion.
 15. The prosthetic device of claim 14, whereinthe bridge portion is sized to engage a femur notch.